I feel like context is kind of important. He was at there representing gamers and YouTube and it’s customary to give the pope a gift that is reflective of your culture. As the culture he was representing was gaming culture, obviously it had to be a game. and what better game than the one that provides a difficult but peaceful alternative. Also a big point of the video was that people see everyone from certain groups based on what they can easily think of and create stereotypes so condemning the whole of the undertale fandom based on an instance taken out of co text is kind of proving his point. Also he admitted he jumped the shark with the sans is Ness theory.