He's got an electrical junction in an uncovered box. That's a fire hazard. And even if he boxed it properly (by removing the outlet box and replacing it with a junction box) it would be against code to plywood over the frame and make the junction inaccessible. To do this properly he could have left the original outlet accessible in a little well and ran an extension cord to it, or he could have run a wire into the back of the box, through the wall, to a new outlet box higher up. He would have had to keep it directly above the old box to avoid trying to snake the wire horizontally through framing, but that would probably be ok.

Now that I think about it, there is probably a code violation in having his new outlet so close to the hvac vent, and also having it horizontal without using a covered floor-style outlet.