What are you talking about? It it his account, and he was the staffer’s employer. Of course he had control of that.
I don’t know if this is the case here, but in at least a few cases, a political person with staff does not create social media accounts, post anything to them, write speeches or press releases, or read or respond to e-mails. And while they may theoretically have some sort of editorial veto over content associated with their name, it’s logistically impossible for them to review everything. Hell, they don’t even read the legislation they vote on. Trump is fairly unique in that he writes his own covfefe.