I disagree with him.
The first point to look at, is what exactly does it mean to be a "true prophet". We get a little help in this department from scripture:
But the prophet who speaks a word presumptuously in My name which I have not commanded him to speak, or which he speaks in the name of other gods, that prophet shall die.' " You may say in your heart, 'How will we know the word which the LORD has not spoken?' " When a prophet speaks in the name of the LORD, if the thing does not come about or come true, that is the thing which the LORD has not spoken. The prophet has spoken it presumptuously; you shall not be afraid of him.
NASUThis passage has several interesting aspects that we could dive into, like the fact that it follows Moses predicting the advent of the Messiah. There are just three things I want to point out: The first is that the penalty for being a false prophet is death. The second is that God Himself allows for the possibility of doubting a prophet speaking in His name. The third is that God allows a provision for telling who is and who is not a "true prophet". That test is if the prophecy comes true.
It is possible that a person could correctly predict something without that knowledge coming specifically from God. For instance I can predict that the Broncos will win their session opener this fall. God hasn't told me that they will win, but there is nothing keeping someone from making the claim that He did. (I doubt God pays much heed to the happenings with the Broncos since they got rid of Tebow) If I got it right (there is a 50% chance of that happening randomly) you still might doubt me as a prophet. What if every prediction I made, not just in sports but in every other aspect of life came to be 100% of the time?
You'd have to admit to a reasonable chance that there was something more at work than meets the eye. Which is where we pick up the story of Balaam in Numbers 22. The Hebrews have just destroyed the Amorites. Balak is the king of Moab and he is distressed that the Hebrews are going to wipe him out because they are great in number. King Balak needs a miracle, so to speak.
Balak sends for a man in Pethor, Balaam the son of Beor. There are some interesting historical and archeological facts about this man that were discovered in 1967. I mention this because his existence is verified independently of scripture, as is the name of the "god(s)" he spoke by. What Balak says to Balaam is also very interesting:
"Now, therefore, please come, curse this people for me since they are too mighty for me; perhaps I may be able to defeat them and drive them out of the land. For I know that he whom you bless is blessed, and he whom you curse is cursed."
Balaam is known for having what he says come true. His blessings really bless and his curses stick. Which is why Balak is willing to pay whatever it takes to get Balaam to curse the Israelites. There is a good deal written about Balaam and his desire for monetary gain. The desire to use a form of spirituality or giftedness for profit is even called "Balaam's sin" elsewhere in scripture. The larger point here is that Balaam could never have sinned in this manner if his ability wasn't real. More importantly Balak, believed him to be the legitimate prophet of a god whose will he could bend to do man's bidding.
Balak believed that spiritual forces could be brought to bear to do the bidding of men. Balaam told his messengers that this was not the case and that he could only do and say as he was directed. This fact alone indicates to me that Balaam was well schooled in the "how" of his office worked. Balaam also had to tell the messengers that he would have to wait to see "if" God would condescend to speak with him. Again this is an indication that Balaam wasn't a false prophet whom God used but rather a true prophet that wasn't in control of the outcome.
We know from historical evidence, and scripture (see link above) that Balaam came from the area of Transjordan and that he was known for his connection with the Shadday god(s). From what I can tell historically, this god known as Shadday (sometimes the name indicates a plurality thus the (s)) is the only god associated with Balaam, his writings and prophecies. We also know or are as certain as might be considered reasonable that Balaam is not a Hebrew. In other words he isn't one of the chosen people of Hashem.
Two questions come to mind. One, did Hashem have interaction with non-Hebrews prior to Moses? Two if He did, was Balaam one of these non-Hebrew prophets?
As a matter of definition everyone from Adam to Abraham was not a Jew. So I'm going to say, "Yes Hashem was involved with non-Jews". Being God's chosen people doesn't automatically rule out God being concerned with everyone else on the planet. The next question is harder because we need to know who the deity Shadday is.
The name Shadday, with that exact spelling only occurs in one book of the Bible. It is in the Book of Job. Job as it happens is the oldest book recorded as scripture. The word Shadday is used to name the god Job worships. It means "the almighty" or "the all powerful one". More commonly "Shadday" is spelled "Shaddai". "Shaddai" is of course one of the commonly known names of God.
Balaam it seems form archeology was a proclaimed worshiper of Shaddai, known more accurately to the Hebrews as Hashem. Do we have any other examples in the Torah of non-Hebrews whom followed the same God as Abraham? Melchizedek comes to mind. So it is possible that there were some followers of the one true God in the world apart from the Hebrew nation at this point in history.
What about Balaam's sin?
Balaam started off right, without consulting God. He told Balak's men he could do nothing apart form what God directed him to do. He even refused to go with them. Then his greed took over. He wanted to go and do as Balak requested for the money.
Because Balaam was a legitimate prophet of God, his words could not "fall to the ground". In other words God could not be false to Himself by letting a prophecy of Balaam fail. It was critical that Balaam not make a declaration contrary to what God wanted, which was a blessing on His people. Which is why Balaam advised Balak how to have God curse the Hebrews for him. Balaam could not prophecy falsely as he was a true prophet. However, he could still get paid by giving Balak what he wanted, having Shadday reach out his hand against the Hebrews.
Balaam sinned greatly against the declared will of God, but he was the real deal.