That's a mistake one makes on their first solo...after that it should be etched in the mind at every take-off.
Agreed but it depends on what else he flys routinely. I was dual qualified on Lynx and Gazelle many years ago and regularly jumped from one to the other to give instruction - on the Lynx, left pedal was power pedal and on the Gazelle it was right. Despite the fact I had over 1000 hours on each, I still said to myself each time on the first takeoff, it's a Lynx, left pedal or it's a Gazelle, right pedal.
In this case, the distraction of having his family watching him and, in his mind perhaps, the thought that the difficult part of the trip had been successfully completed, might have lowered his arousal level for basic flying techniques.