Interesting. I'm not sure what happened there. According to our traffic logs it's doesn't appear that anything out of the ordinary occurred, visitor-wise. Unless it appears that anything undesirable occurred, Dr. Smoo's prescription is that is was a quirk of some sort and nothing to worry about.
There are a lot of things about PHPBB that I either don't know or don't like. I'm working on another project at the moment but I currently am planning to write some custom forum software to use in place of PHPBB, which would cut down on 'quirks' as well as spammers (ideally), so given that plan I'm not too concerned about what it could have been.
But hey, there are worse problems to have than lots of guests on Hamster Central!