Normally a fic like this one-shot goes the followingway.

Equestria appears on Earth.

Earth get's magic poisoned.

Conflict ensues between pro and anti-conversion forces on both sides.

Then Author tracking occurs depending on how much you like humanity as a whole. Yada yada yada.

This fics merely takes two simple facts about the Bureau genre and changes them: first the idea that Celestia herself is leading, or even aware, of the Bureau.

And second, that the earth attacked is a real life esc earth.

No, the rogue Bureau decided to attack Earths belonging to multiple other shows, books, movies, games, etc....and none of them are all that happy about it.

They also don't really do that well at the conquering part.