Alternatively, someone arbitrarily adds your name to his/her ping list. It happens.
Yup, you're right about that. Check my post 17. I don't recall the troll's name, but it was something intended to appear patriotic. There've also been a few FReepers who've gotten into some arguments and people ended up getting pinged to threads with articles with views that they disagreed with. Don't remember who it was though (yes, I know, I have terrible memory).