One of the most pernicious things about the internet is how a single unconfirmed report about something everyone is interested in can spread like wildfire without any further confirmation. Chasing these down is like playing whack-a-mole, and after a while, it becomes so pointlessly exhausting that some sites just shrug and say "well, it could be true." And, yes, Toy Story 3 grossed over $1 billion worldwide. Disney would be insane not to at least entertain the possibility of making another film, and it's obvious they have not outright denied they're working on another Toy Story, either.
But the Pixar brain trust has also been quite clear that when it comes to the franchise that launched their studio, they do not want to mess around: After Disney bought Pixar outright in 2006, the studio canceled a Toy Story threequel that Disney was working on independent of Pixar.