If you traded business cards, it’s not that weird to get a note. However, help the guy out by reminding him of your conversation, when and where, and perhaps something he said that you remember.
Also don’t pressure him to intervene at all; he can take the cue and understand what you are hoping he might do, and if you badger him about it.
Actually, rereading your stuff, you should write to him and say that you saw the ad and it made you remember him from the CFA lunch. Ask him if he knows anything about what they are looking for (since it looks like he’s in the division that might be hiring for the job), and if he thinks you’d be a good fit. As a follow up question, you can ask if there are particular skills or experiences that you ought to emphasize in order to be considered seriously. Be sure not to presume that he knows your experiences… you’re just trying to get a read as to which things their firm is most looking for, so you can play to them in your cover letter, resume, and (hopefully) interview.