Were you even watching his match with King Mo? Mo was practically taking him down at will. You don't kick ass on your back.
Actually you can, and he did. Mousassi IMO should have won that fight, he beat Mo the F up from his back and MO did exactly nothing, nada from the top. It was MO in Mousassis guard getting beaten up from the bottom the entire fight.
mmaswe82 answered it pretty well.
Mousasi kicked Mo's ass HARDCORE in that fight, Mo was battered and didn't land anything on Mousasi from standing or while on top or even any slams. Mo must have hated that fight so much, standing he was getting tooled and when he took Mousasi down he was getting beat up almost as bad.
But srsly if Mousasi read an MMA judging criteria book once he'd probably be the #1 LHW or close to it.