Zero evidence for that theory. People didn't know parasites existed so that couldn't have been the reason for abstaining from pork. But if that had been their reason they would also have abstained from chicken because it is even more dangerous than pork (salmonella etc.). But to the best of my knowledge, no religion prohibits eating chicken. Neither could the Jewish priests who created the rule have observed that people who ate pork got sick more often than those who abstained because they didn't. People who eat pork do not have worse health outcomes than people who don't. Also, remember that 3000 years ago meat was a luxury. The average person would eat meat a few times per month at most.