With a gif maker? ahem.

10 years ago I did gifs with photoshop. By now there should be tons of other software to do animations. I don't think he animated that brick himself, that would take actual work. He probably just used that brick animation and put the cat before it. Not really good tbh. Level 1 is the cat, Level 2 the brick, done. Easily done with photoshop, GIMP can do that too.

If you want to animate a brick like this, you need to create several pictures of the brick in different angles. I think you can let the picture flip with an effect so the physics looks real.