I would generally go "you know that'll provoke an OA right?"
But, you say you've corrected him earlier in the game? What on, OA's he was provoking and suchlike?
And when he's been correcting you, has he been correct?
You are technically in the right in the described case, but that's not really what matters. What matters is; can you play with this guy, and have fun?
Yeah we've been friends for years, more like a good natured argument that he wasn't happy to lose
I clarified his attack several times before this and on previous sessions
He was 1/2 correct on one rule, but only because it didn't go his way the way we were playing it. (Wake from camp when they got attacked, I made them do a check to awake from their deep sleep, he kept failing and I wouldn't let anyone else wake him up which is legal in the rules. He was never hit or attacked)
Other times he was incorrect (4 - 5 times) so this was kind of a "you know the rules then you should know how to switch weapons and do a basic attack"