The obvious thing in this case would have been to link him to his recent comments page and see if he could find it, especially when he'd only made one comment ever. But the details of the request were interesting enough that pretty much everyone in the IRC channel started poking at it, to see if they could find out anything else. That's just what Support geeks do.
In 25 minutes, I found the comment. I was surfing the interest, I wound up in a comm, I poked through a link involving the language in question, I scrolled down through the posts in the new comm in the language, and there was the picture, there was the comment, and there was not the comment back from the original poster.
I still can't believe I managed to do that.