I don’t know his story, but those two responses ^^ strongly suggest that the odd diet was a safeguard against poisoning, perhaps on a pretext of healthy eating. I’ll bet he ate differently all on his own.
I don’t think hobbies had been invented in the 1500s. They’re a luxury of the leisure class and not something for people whose lives consist of labor and a scramble to survive. Nostradamus was a physician by profession, so the Wikipedia snippet tells me, so one may assume that he had interests along those lines.
Even though dining at court means he enjoyed certain privileges in life, he probably had no time or freedom to pursue what we’d call hobbies. Unless you want to count cultivating occult practices such as clairvoyance and writing down prophecies that people still study.