I dont know how but it appears to have happened.
Nor do I. I don't have access to your account, so I can't see what's sitting on the file system, but there is no way the site as it stands should be taking up even a significant fraction of 1GB. You don't have a lot of docs hosted (first thing I checked), your photo gallery is small and low-resolution, the calendar entries (which are probably in a database rather than on the file system) are minimal with maps downloaded on demand from Google, your code rep is off-boarded to code.google.com, etc. I'd be shocked to see 100MB for an actual disk usage for the site, even if the images are improperly compressed and nothing text-based is minimized. There has got to be something stored that isn't part of the site proper, like backups or unlinked files. Since they would count as "file storage", disk space wouldn't be increased to accommodate them. There may also be a considerable log file (or set of log files) somewhere that needs cleaning up.Take a good look at your space to see what shouldn't be there. It isn't the site itself taking up all of that space.