Actually, it's happy because it just went in a time machine to the future, seeing how everything ends and how cockroaches eventually take over the world.
Buuut. since it's a smart cat, it ate all the cockroaches, mated with an african panda bear, and had kittens that look like small pandas.
Then, with it's newly formed family, it took over the world making shoe-tasting muffins!
And the story of why the kitty is so happy. ^_^