The arms went up as requested. Zoro wasn't actually offended (even when his fur bristled, that was mostly just his way; it took a lot to truly get under his skin), so much as keeping Mir in check.
"You're one of the masters breaking in new slaves after the last auction, aren't you? Part of your head is still with them." It made sense to Zoro for Mir to be preoccupied with that, bringing some of that necessary sense of decisiveness and self-assurance into his work. It could be difficult to leave it at home and not take it out into the rest of the world with you, and there wasn't always a reason that you should. "Don't mistake me for one of your pets, asshole," Zoro managed to say in a completely deadpan, nonchalant way as Mir's hands literally mapped out every inch of his body. It suspiciously resembled a joke.