I see what you're saying Charbon, but there is no contact between OW and the H, only via this frenemy.
H could have just said 'oh right' in a totally non-committal way, or ideally, "well tbh old friend, I'm not really interested in if OW 'misses me' or not, I'd prefer to not be discussed." And leave it at that.
This pathetic and frankly nauseating hand wringing of his and bringing it home to 'discuss solutions' would only be helpful if OW had made direct contact, rather than her misguided and wholly unwelcome fishing expedition. He didn't need OP's input when he was planning or executing his betrayal, why should any responsibility now fall on her shoulders.
She was testing his resolution, and tbh, from here, he didn't really pass.
The only thing he should have said to OP is after the fact, I.e "OW tried to send a message via X, but I told him I didn't want to hear it, and that it was very clear that there'd be no further discussion."
If he's man enough to commit adultery, he's surely man enough to put right the wrongs he did. All this pathetic 'oh say Hi from me', and worse putting OP in the situation where this creature has the brass balls to send a Hi to the OP is H's doing, through his utter failure to find the balls he apparently has to fix it.
He needs to rally to his wife's side, and do whatever it takes to fix her image of him, not invite some mangey OW to actually say a single word to his wife.