Interesting legal experiment.
IF, as the student asserts, the prof suspended him for disagreeing with her claims. He should make the same claim against the Koran, i.e. that nothing within its pages can be true.
Should that be considered ‘hate speech’ (done in several localities) then he has a case that the State has, defacto established a religion.
Since he could show that to criticize Christianity (and Judaism, Hinduism, etc. as has been done elsewhere) is acceptable but not for Islam, the State has deemed Islam the only acceptable religion and therefore is in violation of the Establishment Clause.
What only an idiot would believe (when not under militant threats or strong social pressure) is that he was a true prophet. The evidence that he was just an unbalanced narcissistic psychopath is overwhelming.