It’s hard for me to know for certain because i do try to steer away from these conversations with my non-vegan friends to avoid conflict, but i think part of it is the moral framing surrounding vegetarian rather than pescatarian as more of a diet in his mind. He did recently decide to stop eating squid because squid are too intelligent for him to comfortably eat, which i understand pescatarians can do too but i think “vegetarian” just resonates more with him