The first link says that he's a 'celebrity', so he might have felt pressured to sort of fit in with the whole Hollywood, self-promotional crowd and make an appearance at the Lakers' game... you know how rich Hollywood types & famous entertainers like to watch games/'be seen' at Staples Center? Well, this may be yet another unfortunate case of that sort of thing.
However, according to his Wiki-page, he was born in Massachusetts and in the second picture it looks like he is with his wife, both donning Celtics jerseys, so I'm guessing he's probably a Celtics' fan... =/
Honestly, i don't think I would have the 'balls' to try and confront a guy as huge as John Cena about his appearance at a Lakers' game, especially if it was to question his allegiance to the Celtics franchise, his roots, etc. I mean, if he felt offended and then challenged me to a wrestling match on international television I would be probably go into hiding, lol.