What you're seeing is called retargeting. When you visit a site, they can cookie you. Then Google lets your serve up ads to those people you've cookied in the past. Sometimes companies do seem to be stalking you. I see ads for Storm on Demand (a hosting company) way too much.

Companies do this because they think someone who has been to their site and looked around is more likely to convert. It makes sense for them to spend some money getting you to return, than to get entirely new people. (Of course, this may or may not be true, but that's the feeling.)

I suspect Google especially uses retargeted ads on pages where there isn't a good inventory of ads related to the page. That is, they can't sell a good ad based on the content, so they'll sell based on who you are. I more often see retargeted ads (Hi Storm) on fairly lame pages.

Some companies seem to do this really well. Orvis will show you ads of specific things you were looking at in their catalog. It does tend to jog your memory, in a spooky sort of way.

It would be nice to have a "enough retargeting" button on the ad, so you could specify that you don't want to see more of these ads.

So their algorithm isn't broken, it is just annoying you in this case.