I could respect the decision not to change at the last minute, but then don't complain about the instruction... That's my issue with him - (see "douche" above).He is delivering.
Ok, so his grip is wrong. He's given a choice - use the "wrong" grip he's used to, or try a new technique he'll probably only be able to use for a dozen or so shots and less than an 30 minutes of actual gun handling time while the crew films the so-called "practice session".
He may be lacking in social skills, but his decision that "now is not the time to change technique, even if the one I am currently using is wrong" may be the optimal strategy to maximize his winning potential in the challenges.