You quoted it yourself.
"It's only a hypothesis, but I think the bond between Pokémon and Trainer is the key to this new Evolution. But what is this bond, exactly? And why are there examples of Mega Evolution only in the Kalos region? There's still so much we don't know..."
Your problem is that you think the only interpretation this text can have is the one saying that some mega evolutions are kalos exclusive (which doesn't match with the context AT ALL but whatever) when you can also interpret this speech as "the only examples seen of mega evolved pokemon happened only in the kalos region". Yes, if the later was true, then this could've been changed by someone bringing mega stones and mega rings to the hoenn region, but we all should know by now that ORAS happened before XY, so it doesn't make sense for Sycamore to say that if the mega evolutions were already a thing in Hoenn.
The blog states as follows:
"In XY Sycamore claimed Mega Evo never happened outside Kalos so far. "
However, Sycamore does not say that. Sycamore says something else which is much more vague and can be interpreted to
mean that, but can also be read in other ways.
Hence, it is only an error if you look at it a certain way, and the blog's complaint that ORAS contradicts XY by showing Mega Evolutions outside of Kalos is invalid, because it was never concretely stated that there weren't. If one chooses to interpret it to mean that there weren't, then that is the interpreter's problem, because
they are the one who is insisting that a problem that needn't exist, must exist. No one is holding a gun to their head and forcing them to read that line so literally.
To give you an analogy, let's take what Sycamore says, and rework it a bit for a moment:
"And why are there examples of clouds only in the Kalos region? There's still so much we don't know..."
If somebody were to say this to you, you wouldn't seriously think that clouds aren't found anywhere else, would you? Not even clouds of other varieties?
Never mind that Sycamore's line is a comparatively inconsequential thirteen-word sentence in an
ocean of far more important data and dialogue, so all of the blog's boo-hooing over how it has somehow ruined the Pokémon timeline (which, let's face it, isn't *really* that important to begin with) forever is melodramatic, unnecessary, and highly overblown.
Also, calling particular attention to this:
Your problem is that you think the only interpretation this text can have is the one saying that some mega evolutions are kalos exclusive (which doesn't match with the context AT ALL but whatever)
So, you know what "my problem" is, huh? Odd that the interpretation that you say is mine is not one that I have expressed in this particular thread thus far. Not sure why you feel the need to be so personal, but alright.