Two quick thoughts.
One is why talked so long about Jesus and not about other Gods. Being in America it is sensible that Jesus gets more air time since Christianity had a massive effect on the formation and culture of the USA. That doesn't excuse preaching basically, but it does justify a longer reflection on Christianity than one would give, say, Confusianism. It is an unavoidable fact that the USA while moving to a "post-Christian" setting has a history as a mostly Christian nation. Again though, doesn't excuse preaching in a Community College.
Second is on Jesus historically. There is enough historical evidence to say reasonably that Jesus as a human being lived. The Josephus text you are refering to is a complicated matter. There are two references to Jesus in his writings and one seems legit, the other not. He mentions Jesus as a Rabbi that lead a Messianic sect which is the accepted notation. However, there is another mention later that refers to Jesus as the Messiah (I think) and that passage is believe to have been added later. Also, the Roman historian Tacitus mentions Jesus as a person in the right time and executed by Pontious Pilot. Other evidence exists but this not the time or place for. I'm just saying that arguing the historical existance of a Jewish Rabbi named Jesus is not worthwhile. There is enough evidence to say that a Rabbi named Jesus lived in the 1st century and was killed. The rest of the New Testament and whatnot, that is another matter. (Luke is shockingly historically accurate actually but that is not here nor there.)
Now, for what I think you should do.
If this is an isolated occurance, let it go. Annoying, sure, but whatever. If it happens again, talk to the professor about how you feel that his lecture is off-putting to non-Christians. If he doesn't listen, go to his Dean with the same complaint. Don't argue though and don't try to disprove him. If he really does believe the Biblical account then a student telling him he's wrong isn't going to sway him. If anything you'll just make it worse because you'll feed a potentially hostile "I'm being repressed" response. So, like others have said, let it slide unless it happens again.
I completely sympathise. I'm taking a Faith and Film class at my school and I get weary of having to couch everything in Christian terms. The difference of course is that I'm at a Christian school but it is still aggrivating. At least you don't have to listen to it. I do since I'm in a religious school so count your blessings.
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