Insulting him and telling him he shouldn't ask for money he is clearly owed because of a mistake we've all made. Actually, that second part is an insult, too. So, really, just being incredibly insulting.
That you wouldn't ask for the money is irrelevant. We're not required by any law, moral, or ethic to go through life as a doormat. At this point, money has been stolen from him, just as if they'd taken it from his bank account. He is owed that money, and entitled to ask for it without you attacking him for it.
The difference between me and this guy is that I wouldn't've turned around and asked the company for a bunch of money afterward.
And what, exactly, do you think I owe him an apology for?