I'm not exactly sure what you are getting at to be honest, and quite frankly not sure I want to know either.
He's making a mint out of scaring you lot silly
Also he's claiming or trying to give the impression of having some engineering knowledge when all he has done is cut the plastic from a plug.
Now if he were to come up with a proper calculation of typical electrical conductivity through these pin connectors, billions are in use so it should be readily available, then calculate the energy given out through losses, calculate the heat conduction into the plastic reduce it by the heat lost through radiation and convection from the socket, if he then assumed a properly seated socket and it heated to the plastic melting point, he could then make a valid conclusion.
Obviously he would have to also do sensitivity studies and probability analysis to assess how stupid someone would have to be to fit the plug in such a way that it could generate sufficient heat to melt the plastic.
Just looking at those pins, there is a lot of static air around them, they would have to get extremely hot to melt the plastic.