not to take anything away from it,but he pushed off the cage with his foot,is that legal?
Yea it is
have seen people do it before for other moves like superman punch, never heard anything about it being illegal.
Legal 
It's incredibly legal. You can push off the cage, you can't grab it.
nothing in the rules says it's illegal
why the fuck would it be illegal? it's not like he grabbed on it or anything, he just pushed off it. Gina basically did the same thing with her superman punch to Cyborg.
Belcher superman punch vs. Akiyama.
Same striking coach as Pettis, not coincidentally.