Why might someone take a picture of you in public?

This person who I refer to was not FULLY a stranger, but for the most part. I was in a grocery store few years ago when a guy I used to see at a bar sometimes walked in. He stopped shot when he saw me, in the front of the store. I am pretty sure he recognized me, but we don't really 'know' each other. I believe he is married, which sucks b/c I always thought he was quite attractive. So a few more minutes after walking around in the store, I turned my head to look behind me, to see if I still saw him, (in the store) and he was not too far behind, and was taking a pic of me. I just turned around quickly to my front again and kept walking. I didn't say anything but always wondered why someone would snap a pic randomly. Perhaps he wanted to trigger his memory b/c he may have recognized me? He always seemed very kind and WAS kind to me at the bar in the past, (even offered to help me once when a drunk guy was near me) so I don't believe it was for any pervy type reason, to take the pic. I still wonder though now a few years later.