We can't really say that for certain. It is without a doubt possible, or, as another idea goes, it was intentionally coded and cryptic in order to more safely communicate with churches and other followers. It's like Moses' burning bush. Could have been psychedelic drugs, it could have been entirely made up. With Paul's ride to Damascus, was his vision a sign of a psychotic disorder, the result of a psychedelic drug, or did he just make the whole thing up? This puts us in a position were we can do nothing more than speculate, and even then we must realize that ultimately we do not actually know.