Theory 1: Chris only blamed himself because someone he wanted to curry favor with told him to do it. It's like the time he made that video professing that he didn't hate the Xbox anymore--not because he looked back on his actions and thought "I was in the wrong, and I must apologize", but because he thought "Hmm, yeah. If I make da video of me sayin' I don' hate tha hess-box anymore, den Jackie dere will HAVE ta consider havin some hanky panky wit me!".
Theory 2: The idea that someone at the Game Place was the fictional "Prime Troll" isn't a recent idea. Megan was even on his list of potential suspects, but Chris eventually became convinced that it just had to be Michael Snyder and Megan was just an unwilling pawn at the worst. However, this all changed at some point during 2012. I assume that Megan came up in a conversation and Barb revealed that she'd overheard her telling Snyder about how Chris kept making unwanted advances on her. This had a profound effect on Chris--his personal narritive went from "Snyder banned me because he hates autistics" to "Snyder banned me because MEGAN WAS SPREADING LIES ABOUT ME? OH MY GOD SHE WAS THE PRIME TROLL ALL ALONG!".