Perhaps they use a "guess-timation" method where they take an average of "actual" meter readings spread over time. That's what they do in my area when they can't access the meter for reading. How convenient that they usually come for elecrtricity in the summer and gas in the winter. (Usually at the high usage points.)To your benifit, they took their "actual" readings during a low current use stage. Be advised that the difference will show when they get another actual reading. Try to avoid it as best as possible.
Then again, I could be waaaaaay off base and you're just one of the lucky ones. Who knows? I'm gonna smoke another spliff and figure this thing out.:rasta: