pingback question

Hi –
I’m quite new to all of this so I apologize if this has an obvious answer!
Yesterday in my comments I had two “pingbacks” from other sites — I get that this means a link was placed to one of my posts on that site. However, it wasn’t that someone was referencing my post in their own, but that my site had been somehow generated in a list of “related posts” at the bottom. In fact, the article wasn’t even relevant to my site — it had just picked up on a keyword. Is this spam? Should I mark it as approved? How does my site end up in these “related posts” lists?

Thanks!