omg puns why
But yeah, ORAS makes it fairly clear that it (X/Y could still possibly take place in the same universe as Gens 1-5) takes place in a separate dimension from the rest of the series. I've even heard the one about how even each game cartridge could be it's own parallel dimension.
It just really spawns though from the fact that Game Freak was strangely short-sighted in writing Mega Evolution into the story of X/Y in a way that made it sound like it was a Kalos-only thing, despite them knowing that they were both going to make ORAS and continue to have Mega Evolution be in future games, then realizing that they created a plot hole and had to patch it up somehow.
I did learn though that Ash references Minnesota in the 1st Pokemon movie though--did not remember that line being in the movie at all.