So where's Reek at?

http://www.justjared.com/photo-gallery/3797872/game-of-thrones-fight-scene-season-7-spain-34/

http://www.popsugar.com/entertainment/Theon-Euron-Greyjoy-Game-Thrones-Season-7-Set-42638920?stream_view=1#photo-42638922

He's fighting back, he even KOs the guy as you can see in one of the photos. This is no Reek. Reek would let him punch him into unconsciousness.

This is from 701, and when Theon reunites with Jon (episode 5), he's in charge. Front of the boat, even helping the guys bring the boat ashore.

Looks like the fight escalated from an argument, maybe fight for command.