There isn't a proof at all....
It isn't even a rumor its speculation by some one on what ever site that was....
its like this..
"MS to purchase a new studio"
random dude1: "It could be Naughty dog"
random dude2:"OMG randomdude1 said it could be naughty dog!!!!"
random dude 3:"OMG!!!!*creats a article MS to buy naughty dog.*"
and thus a mere speculation turned into a stupid rumor has become virale