I know its a percussive strum, is he up stroking the chord as he percussive strums it to actually play the chords?
yes, that and he gets chord progression, and using riffs for fills.
There's more happening there than the video shows. In the first part, you have the strumming, but you also have picked notes - they're either done with a pick or fingerstyle. I don't see him playing that part. He's just doing more of a percussive strum.