It seems as if there is a 220K pull-down resistor on analog pin 0
They don't connect a resistor as such, but analog input pins do have an impedance which can affect your readings.

If your output impedance (the resistance of your resistors) is within about a tenth of the impedance of the input pin then you will (and have) noticed skewing of the results.  This is normal.  The input impedance is somewhere in the region of 1MΩ - 10MΩ.

You have to keep your output impedance to a value below the order of a few tens of kΩ to minimise the effect the measuring of the value has on the value.

If you want to measure higher resistances then you will need to buffer the voltage with a very high impedance op-amp buffer.

Incidentally, your volt meter probably has an input impedance in the region of 10GΩ - around 1000x higher than the Arduino's ADC.