Can someone explain the camera movement at 0:21?

As mike say's it's not a camera movement but if you ask to know how this small sphere jump, you can learn more here about squash and stretch https://www.schoolofmotion.com/tutorials/squash-stretch-after-effects

This is none : )  Camera movement, that is.

If you are taking about the accelleration of the object movement - look into the basics of the graph editor. This is  a simple accellerating speed curve.

See:

Fine-tune animations |