I never heard of the rumor, that the N7 guy was the antagonist, and I've been following the andromeda news for a while now. Seriously, who said that? Just recently it was stated, that the N7 guy could either be the male protagonist or part of the ryder family, like your brother if you're playing femryder, for example. Somebody link me the antagonist statement, and no more "leaks" by shinobi or other users please...
See above.
I honestly believe it started several weeks ago when I casually said, "He could end up being an antagonist, of sorts." I developed the idea a bit, but not much. My reasoning was that BioWare had previously told us that he was "not the PC" but "is plot critical". The idea caught on, and now it's like an infection we can't shake. Once the trailer was released, the new info, such as the "sibling angle" was incorporated.
We actually know very little for certain. The upcoming novel "Andromeda Initiative" will likely start answering our questions. I hope it's not delayed as the game was.