And as I explained, that “chumra” is Am HaAratzus. At least the people in the gemorah had logical chumros!
I don’t think this has anything to do with being smarter than chazal. For one thing, I don’t see this as a chumrah at all, but a private hanhaggah. Would you be upset if he decided to button his shirt from bottom to top because he wants to be oleh b’kedusha?
Second, this doesn’t fall under the category of a gezeirah sherov hatzibbur yecholin la’amod bah, because he is not trying to establish this as a minhag for the tzibbur but his own private hanhaggah.
Third of all, I imagine that not eating pizza is not in direct mourn but to facilitate a somber atmosphere in his house. For some people, pizza is a fun food.