My sedevacantist friend does not know if they got a Novus Ordo annulment and when he asks about it the friend tells him curiosity is a sin.
Red flag! Marriage is a public act and nothing wrong with asking about the status of his marriage. Turning on the friend saying he is the ONE being sinful makes me think this person knows what he is doing is wrong and but won't admit it. What is he hiding by not answering? If there is nothing to hide, he would give a simple, truthful answer to his friend.
Unfortunately today, there are a lot of people in invalid marriages or permanent states of adultery. Yes, even some Trads.
I think you have a moral obligation to notify the priest and let him deal with the couple.