"Pietro's friends aren't Avengers in his world. They're mutants. I think he said he and his boyfriend are in comic books, but their friend is also in movies. But not our movies." The only thing powerful enough to mess with reality on this level was the gauntlet, but even that didn't make sense. Not when Steve was there too, not when they'd ended up in a world with the same problems Thanos had supposedly been trying to solve.