It was knocking really bad and well this is what we found when we pulled the top off.

Running too hot and or lean.

Most common cause for a black piston is blow by because of worn rings. Your looks like the piston is pitted so I would guess it's been running hot and lean.

What is it from?

Looks like a dirt bike.

That pitting is detonation. Likely detonated.. Stuck a ring which is why you have both light/tan and burnt/black colors. I would check to see if the timing adjustment came loose, or if there is dirt in the carb (if it's stock and if it's a YZ125 or equivalent make like it looks). It's not way lean as it would have burned through the piston. It's pretty gnarly what happens when you pinch a fuel line at 12,000rpms.

It's off of a honda pilot. He said it was running slightly lean but not bad. He thinks the ring fused and caused the loss of power.