You don't know how or what just happened, but honestly, it's best not to question it. Looks like he's grown himself up to be even taller than the skies, and he's just unaware of what is about to happen to you as he's about to take a step. After all, you're smaller than Harry, and you can tell he doesn't even know where you'll be at after this...

This is Version B, where he's bigger than the skies. The A version is with you being the one shrunken down.