World English Dictionary
glitch (?l?t?)
— n
1. a sudden instance of malfunctioning or irregularity in an electronic system
I'd say this definition sums it up pretty well, with the numbers mentioned being both sudden, irregular and in an electronic system. My field of work doesn't cover this type of thing, nor do I claim to be educated enough to make a guess as to the cause, but I reckon the forum being electronically driven fits into the glitch category pretty well.
Being a cynic and a sceptic, I find it hard to believe that the big wet had prompted everyone onto the forum for just one day, if these high numbers had lasted for a few weeks or even a month, this theory might have held some credability.
Obviously by a couple of posts above I'm not the only one to believe the numbers were somewhat dubious, nor am I the only one to believe in glitches.