Any idea how Zillow calculates values or rents for multifamilies?

[Johann Jells]

A while back I actually "claimed" one of my properties, a 3 family rowhouse, and entered in the correct data to see what would happen to the "Zestimate". It's now $827k with a rent of $2300. WTF? Regardless of the accuracy of the price, are the GRM's that high, or do they simply pull this stuff from their rear? That's a GRM of 30! It's 2 2br and one 3br, actual rent roll is $4750.