Nick,
It appears that you successfully posted the even in the calendar, however as the calendar is not a 'forum' per se, it does not send out a message to members.
I think someone has already copied your calendar item into the Bristol News forum, which will send out to all who are subscribed to that forum (which is hopefully most people).
Regards,
Kevin
PS. I moved your question about using the calendar into the 'About this site' forum, which is where it belongs
