It is a smooth trick, perpetrated by Handejector and his operatives. It makes anti-gun organizations throw away perfectly good money and internet coverage by putting ads in a place where they have absolutely no chance of influencing anyone. Sort of like Krispy Kreme running an ad in a dieters magazine.
This has been covered numerous times. Let's hope that this is the last.
We do not have control over what Google ads show up. They are random based on the chatter in the forum. If someone is talking about a specific topic, there will likely be a related ad pop up at some time. Just search the forum to see how many threads contain the name of the individual in question and you'll see why that particular ad shows up. If you have several threads running about a particular brand of root beer, sooner or later and ad will show up for that product.
If it's any consolation to you, take solace in the fact that he's spending his money for ads that play to a hostile audience.