I wouldn't worry about it. So long as you had unlimited mileage on the rental (and hence aren't being charged for the miles), nobody will care, because anybody who actually checks will understand that you didn't actually drive 2k miles, particularly if the error is on turn-in (i.e. they overstated the mileage at turn-in), in which case the next turn-in will show negative mileage.

I once had a rental where the return clerk fat-fingered the mileage, and it showed slightly over 10k miles on the rental (should have entered something like 12,250 at return, actually entered 22,250. Never heard anything about it.