I saw multiple sites reporting this with a headlines saying Disney confirmed that all movies in the Pixar universe are connected, which I thought was very misleading. Disney released a "cute" video, I believe on the Toy Story Facebook page, showing many of the Easter eggs in the Pixar films. Like Ryan said, the Easter eggs has been known for years and in my opinion the video released is simply a "highlight reel" to show all them, like characters or objects from one movie hidden in another. I don't think there's any confirmation from Pixar about the connected universe fan theory.
A google search will get plenty of hits, but if anyone is interested, around 2013 a elaborate fan theory came out that tried to connect the stories of all the Pixar films into one universe. The very basic idea is that Boo (Monsters Inc) spent her adult life trying to find Sully, invented time travel/portals and Boo is actually the witch in Brave, disappearing from Merida by opening a time portal, continuing to search for Sully. Along the way, humans have destroyed the earth in Wall-E, giving rise to a world where autonomous, intelligent robots control the Earth in Cars. There's a lot more to it than that, but that's the very short version.