The Mooshimeter’s officially accurate resistance range is above 10 ohms. This is because there’s a little bit of internal resistance in the meter that can change over time. Specifically, there is a high voltage PTC in the resistance path for protection, and its resistance increases slightly every time it’s used (every time the Ω input is overloaded), which is probably what’s adding the extra 1.5 ohms in your case.
The resistance readings at low values should still be accurate if you perform a zero first. You do this by tapping the “zero” button. It will turn green indicating the offset is being applied. To stop applying the offset, tap it again.
Let me know how it goes, best