My Guess is that you have something called Ghost Export and the Electronic meter is registering it.
You say, you don't export, but there is something called "Ghost Export". I have noticed that in our setup and on the day the meter reader comes we have a FAN running on a circuit that bypasses the solar and thus make the meter go forward ever so slowly, the rest of the house is "powered" by Solar.
Edit: Must add that we still have a Spinning Disc Meter, if we get a Electronic Meter, then we have to run that Fan (on that separate Circuit) from Morning till evening. I am thinking of getting a LOW wattage ice maker and use that instead of the Fan 😉