See I think that's retarded... Apparently Sony also aren't allowing a full investigation into it, then come out with this? But then again, think about it: Hack into somewhere and leave someone else's card. Like if you break into someone's house, and leave a card on their table: "Sorry for stealing your shit, my name is Matt Bobfranko". Likelihood of it being 1) someone just dumping that file there to deflect the investigation off onto a known "menace"?
Also keep in mind, there's always splinter cells of Anon. Not like they all got together and went "OLOLOL LETS DO THIS", considering the main attack was a DDOS, and when it affected people playing PSN, and not just the Sony websites, they reined it in so that the customers weren't affected.
TL;DR, it MIGHT have been SOMEONE who calls themselves Anon, but it's not all of them.