Am I just bad at conversation, or do these people have stalker tendencies? [I Am Bad At Conversation]

Occassionally I'll get a random message out of the blue from someone I chatted with like two years ago, and they'll pick up that conversation as if there wasn't a huge gap of time in between. Like, they'll bring up very specific details about the last thing we talked about, and I'm sitting there in the dark, because I completely forgot everything. It's always those people that have nothing on their profile page too, so I have no way of reminding myself who they even are.

Am I just that bad for completely forgetting a person's existence, or are they just being stalker-ish? I mean, are they really re-reading every conversation as a refresher before they start again for whatever reason? Also, why bother? If we had a short, meaningless conversation two years ago, and haven't interacted since, what makes them think I'm interested in starting that up again? Honestly, it's kinda creepy.