I think they will not (should not) add somebody to the list with only one request from one forum. I only checked some ip's, and most had lot of activities registrated.
Others with shorter lists had comments like 'no activities in the las 9 weeks'.
The page does not explain if you can add 'somebody you hate' with only one record, as it also does not explain how and when they remove the records - something basically - , as i suppose that most spammers do their work from dinamic ip's.
But if spam is a problem in the forum, i believe it's good to trust their banlist. If some user get's registered by error (or if you hate him), he can always register with a new name from a friend's ip to complain.