Probably. That table can get very large very quickly.
I'd take this as pretty conclusive evidence that this is the reason.
This is normal and expected.
The purge should always make the database smaller. If it doesn't then something has gone amiss (or there was nothing to purge).
If I were to clutch at straws for an explanation I'd suggest you possibly had some kind of error relating to this table and your 'abrupt error (Server Internal Error 500)' caused the server to restart and in doing so initiated an automatic 'repair tables' and things are now back as they should be.
Cheers
Rod.




