When you are ready to discuss it with your partner, perhaps do it in a “that was odd, what do you think?” Rather than fait accompli.
It sounds like your partner has had years of conditioning from this man. Realistically, if you are to have any chance of success in helping him to see how controlling and inappropriate it is you need to do so by gentle questioning to get him to think it through himself and provide an opportunity for him to raise any doubts of his own.
If you tell him your (and our) views that it's bullying, controlling, inappropriate, grooming, etc, he is highly unlikely to listen. He will just go straight into defensive mode and not absorb or entertain anything you're saying. Whereas if you raise it through questioning it will get past those automatic barriers and sow seeds that will enable him to undo the brainwashing he experienced as a child.
Because grooming is conditioning, it is brainwashing. Bullying, controlling (abusive) men get their partners or children to accept their behaviour (and therefore not tell anyone) by conditioning them to believe it's normal, to believe it's acceptable, to believe if it makes them unhappy or uncomfortable it's just because they're oversensitive, to believe it's what's happening in every other home in the country.
You can't begin to undo that just by rocking up and announcing "hey, this is wrong!". It would be like somebody telling you the sky is actually yellow and always has been - you'd tell them not to be so ridiculous.