You only ever really slide to avoid a tag. Feet or head first on the ground. Sometimes when the throw has definitely beat you, you just plow through the catcher to hopefully make him drop the ball. That's painful, a little dangerous, and doesn't work very often.

Catcher's physically block the path to home plate. In this case the catcher was standing up. There was NOWHERE to go to avoid the tag or get to the plate, since the throw beat him there.

So he just used athleticism to jump over the whole damn guy and score a run.