Yeah, if it's actually a demo I wonder how it was found. You'd think that, at this level, Taylor would be way beyond letting stuff like this leak, but then again she probably didn't intend on doing anything with it so it might be not as well-protected as any new songs that didn't make the cut for 1989, for example. This is all speculation, of course, because I don't even know if it's legit, but yeah.
To be honest, the 'shake it aw' part makes me cringe haha It's so weird, and it makes me wonder if this could actually be some buried background vocal someone found while taking apart the tracks/stems of the original song. It has some quite different things, though, so that kinda undermines this theory.