Yeah, this is highly context dependent. If a guy meets a new couple, they chat for half an hour, and then half the couple excuses themselves for five minutes - in that case it’s perfectly normal to take the opportunity to say “hey, you’re pretty lucky.”

But if you meet the couple and immediately congratulate one half of it like the other isn’t there, I’d see that as insulting. Not because I think you want to bang them, but because you aren’t even treating them like a human.