Not quite. They just took the whole thing, slapped something over the back-end to make it compatible with wordpress, and left Flarum itself like it is. There is no real change at all (It feels somewhat slower, though.)
Why not make a plugin for Flarum instead? Because they also want the attention, that's all. Of course the whole thing is perfectly legal, which is why no one can actually take it down. It just feels really silly to use a beta software for what they had in mind.