Similar plays should result in similar calls. Maybe he didn't trust you to remember that in the heat of that play. Yes, it was out of his area, but my guess is he grabbed it b/c it was a similar play and he wanted to make sure that you (as a crew) had
consistent calls on both teams at each end of the court.
I agree that it would've been better if he'd let you make the call. But without having worked with you before, he may have been unwilling to give you first crack. He probably already had in his mind to find the first thing that looks close to a charge and put a whistle on it; especially if, as you say, the first one was marginal.
The worst thing would have been for him to have a charge on A1 on that marginal call, and then for you to have a
block on a similar play against A2. Now you've got Coach A screaming about how come it's a charge against my kid on this end and the same play is a block against my kid on that end?
Sounds to me like your partner was ensuring consistency, and just didn't trust you
yet to make the similar call. Talk about it when you work again. Ask him about that particular play, if you didn't already talk about it. Tell him you'll try to remember what's been called and call the game the same way. Maybe he'll put that faith in you and let you make the charge call next time.
Good luck.