It happened when I made the post. It's just creepy!
Can't have been me logging in at work then, I'm nowhere near there at that time (11 PM).
I think I've seen Cat do something similar.
"koko_99_2001, koko_99_2001 and Deloria are viewing this topic". 
IIRC, the database stores what members are doing for 15 or 30 minutes. So, If you watch a topic and leave it, and return within those 15/30 minutes, and the database is 'bugging', you might show up double.

I'm just taking wild (un)educated guesses though.