Fear of Heeling
If I understand your story correctly, the combination of the gust heeling you over a bit more and the powerboat wake hitting the leeward side of the rail made for a lot more water than usual shipping over the gunwales.
The bad news is that everyone aboard may have experienced the need to really hold on to avoid being thrown out of control, and maybe they didn''t realize just how far over a boat can go. The good news is that the boat handled that and she came up on her feet just fine. What I would hope to take away from that experience is that it takes a lot more than that to capsize a boat.
Having said that, I don''t have any advice for how you get your crew to look at it that way. Good luck and smooth sailing!