Plus, Mewtwo was put there for a reason. If either of the two encounters warrants being disregarded, it's the one in Kalos. Red encountering Mewtwo is the logical follow-up to Red becoming the Champion; even Pokémon: Origins included it. Mewtwo's presence in Kalos is little more than marketing since it's appearance isn't even explained despite the contradiction between it and previous games.
Regardless, none of this - absolutely none of it - changes the fact that people can be interested in discussing these events as an accepted part of the story without being "worried" about it or "losing sleep" over it. It's just a topic of interest and there's no reason to shut it out just because you're not as enthusiastic about the subject.
Hildabert were busy looking for N and likely didn't make it to Unova in time to do anything of significance. The time between Ghetsis using Kyurem as a weapon to attack Opelucid and Ghetsis' defeat isn't a terribly wide gap, and N would be quicker to respond anyway since he can communicate directly with his dragon.