Honestly I don’t understand the insistence some people have that any way other than their own is against the rules.
I think their obsession with metagaming sounds boring, and sucks some fun out of the game, but it’s not against the rules (nor is it in the rules) so it’s totally valid as long as they all buy into it.
If they want to reciprocate and say our way of playing is not fun for them, fine. But, man, this crazy obsession with calling it “cheating” is just f%#€ing weird.
If the DM has stated that metagaming is not allowed or should, at least be kept to a minimum then the players should abide by that as part of the social contract of the game. It doesn't matter what you label it, if metagaming is discouraged do your best to avoid it.