PSP Fanboy is a subsidiary of Joystiq, so it's somewhat credible. And yeah, a homebrew thing is definitely more likely. The first pic in the post were images of Halo 2 pasted onto a PSP screen. No 'real' Halo game would come out on the PSP.

There was something like this on the DS as well. (This blog is of the Head Nintendo Guy at IGN, so he's not pulling any legs)