Geoeric, let me try to explain in simpler terms:
There is a current flowing through the soil. You know this because there’s a voltage across the soil, and the soil has a finite resistance. Ohm’s Law tells you that current equals voltage divided by resistance.
The Mooshimeter uses a very small test current in resistance mode. This is a sign of a *good* meter. Cheaper ones may use a larger current, and normally this is not a good thing.
The relatively tiny test current of the Mooshimeter may be overwhelmed by the soil’s own current, and that disturbs the resistance reading. You can test the truth of this by switching the Moosimeter’s leads round and seeing if you get a different reading.
Finally, just because a cheaper meter gives you a believable resistance value, that does not mean that you have made an accurate measurement.
And no, I’m not associated with the creator of the Mooshimeter.