Ask HN: Does Facebook sift through your image cache?

I got a strange contact showing up as a friend recommendation. The wierd thing is I don't know the real name of this person and cannot figure out how facebook got it! (And I am pretty sure the other person doesn't know my real name either). So the only possibility I can think of is FB looking through my browser cache or something and doing a face/image detection/recognition of sorts. Any idea ?