Probably a promise not to mention the subject was an integral part of the negotiations that brought him the interview.
“Probably ...a promise not to mention the subject...”
More probably ... Chuck even thinking about asking it never occurred ... no need to make promises.
Oh it is even worse than that. Their camps coordinated the optimal ways to protect her and decided an interview while ignoring the subject would help to delegitimize the issue. He didn’t make a reluctant concession at all he wanted to do whatever he could to help her.