Afaik other than some bans, only matching of your forum account to your XLR stats is done via IP. That matches all your stats or none of them, and when it mismatches you, a later re-match restores everything as though it never mismatched. It merely sets which stats to display in the forums next to your posts.
If you weren't at home, was maybe someone else playing on your computer?
P.S.: As for in-game nick, pretty much everything on DSWP is immune to nick changes and/or coincidents (with perhaps exceptions such as bind x "!slap someplayername" .cfg lines).
