I'm a ratings expert. Just ask Mashanator.
Probably just a game you had ongoing and forgot about and they resigned... that's my guess anyway. They don't recalculate stuff. If you had no games going on then your rating shouldn't have changed at all.
Rating changes
Sort:
Are ratings recalculted at differant times - I am not talking about after a game where you gain or lose points. My rating seemed to jump twice in the last 6 weeks by 15 points or so right out of the blue for no apparent reason.