Oh sheeeeeit this is a vipers nest of a questionnnnnnnnnnnnnnnnnnnn...

Your professor certainly represents one strain of revisionist thought regarding early Islam, albeit one that's a slightly older (50 years old maybe? Sounds like something W. M. Watt would say).

The other one (the one I'm vaguely more familiar with) was that early "Islam" was actually part of a long standing Judaizing priestly (not rabbinic) monotheism which crystallized around the turn of the 7th century around Muhammad, although there were other prophets which arose at the same time, so perhaps Muhammad just turned out to be the one that survived out of that particular tradition and time frame. This argument is based on recent epigraphy and archaeology coming out of Yemen, which showed a monotheizing tendency occurring a full century before Muhammad's mission.

Bowersock certainly made a recent case that Muhammad was perhaps operating within the confines of geopolitical tensions between Byzantium and Sasanid Persia (namely the last great war of 602-628) but I mean... that's a very traditional sort of history which presumes a machiavellian political role for religion. And while religion certainly has that element, to say religion is only a subset of politics is just a bit... reductive.

On the other hand, much also depends upon your standpoint with the recently carbon dated Birmingham Quran manuscript, which was supposedly written in 650. If the writing on the manuscript genuinely was written in 650, it would settle a lot of debates about the time frame for the evolution of Islamic tradition.

If you believe in the 650 date, then Islam as we know it was codified rather early, and we could perhaps trust that the Quran is a mostly accurate reflection of what Muhammad was "going for" when he set down his faith and practices.

If you don't believe in the 650 date, then much of what would become "Islamic tradition" may have been no such thing when Muhammad and his believers were conquering out of Arabia. However, it would remain a tossup as to "what they really thought" because the sources from within Arabic tradition don't occur until a hundred years later.

Personally though, I've kinda enjoyed the position that my professor made about what he thought Muhammad's early beliefs were: That they were judaizing (but not jewish) monotheists (who also had a position in their belief system for Jesus, but not as the son of God), who believed the end of the world was coming, and were harnessing arab tribal energies into a conquest for everyone's salvation (a relatively gentle conquest by ancient comparisons), and after they took over Jerusalem, proceeded to FINALLY build the 3rd Temple as the Dome of the Rock, because as The Final Chosen People, the end of the world was nigh, and it was about time they fulfilled their prophecy.

Then they had to fail to take Constantinople and screwed the whole thing up, thus deciding "I guess we'll be Muslims now..."