The guy knew his punch had been stopped and Phil was flanking him so he tried to pivot and re-face. So Phil transitioned to a Lop Sau to maintain control of his lead arm and punched him. "Stiff Man Sau" vs. "Actual punch" amounts to the same thing from Phil's side. This could very well have been a demo of how to defend against a simple "forward intent" lead hand punch. So just what do you see as the problem?
More of a potential problem, or potential counter.
I wish I had a video to respond with but I don't. Anyway, in the VT I train, the response would be to let the lead arm yield or bend with the lop, while stepping forward and to the left ( going with the force) while simultaneously turning to face the opponent and firing a rear hand punch. We call this step-turn falling-leaf step. We train it against just such a hard, downward jerking lop-sau. For people that know the old WT curriculum, it's in the Lat-sau section 3 drills and in the Chi-sau section 2 drills. Done right it uses the force of the opponent's lop to accelerate your counter.
...The basic idea is not to resist, stiffen and pull back, but to flow with the force, moving forward, and to punch when the hand is free -- in this case the rear hand.