It's not a dive by Muirhead. Napier might think there's not enough contact to warrant the penalty, but the defender is caught wrong side and puts his hands on his back. Obviously he doesn't give everything to stay on his feet for as long as he can, but there's a big difference between that and a dive. The push on his back makes him lose his balance and he's hitting the deck either way. The reaction is silly - he's done that far too many times this season. It's not going to get you anything. He needs to stop that. I still hope he signs next season; for his faults, he's still a good player at this level.
Napier is highly spoken of as a GP down here, and apparently is a nice guy, but he's a really poor referee. It's clear, though, that the standard of refereeing at the moment is terrible. It's a problem that goes pretty deep.