From what I've been told about 4chan leaks, users have trip codes that go with their posts. The original leaker had a trip code that the "new" posts, about KOS-MOS and Reimu, do not have, therefore making it impossible to say if it's the same poster.
If you were the same poster, and you wanted to get more credibility and be believed, why would you not:
1) Provide the code names for Terry, and the unannounced Fighter #5
2) Have the same Trip code
Chances are, the answer is because it's not the same dude. Thinking this is fake.
Folks, half the reason people make fake leaks is because the fanbase eats them up. Every. Single. Time.
EDIT: Let's also reflect on the fact that this dude would have had to have gone from just knowing the codename of the character before to now literally knowing content in the post-fighter pass lineup.
That's a big jump.