It's obvious from Machio's fretting that he can play guitar to a degree , but certainly not enough to play that solo at the end of the duel (specialy when Vai's around).

If you're sick minded enough like me to watch the video thoroughly and analyse Machio's fretting , you'd notice that he's just moving his hands around the positions he should play , but his fingers aren't moving right (as Vai) ... Even that legato line before the solo starts looks funny when he plays it.