Because the diagram on that page:
shows "Voltage Out" (i.e, your ADC input) at the far right, I'm going to assume it's asking for a minimum output current to ensure stability, therefore, you need a resistor of 65k or less resistance (500uA @ 100% humidity) or more current) to get a stable output. To put it another way, 65k is the largest resistor you're allowed to have there. If the resistor was internal to an ADC block, I would interpret it as the minimum resistance/impedance of the ADC.
Typically, power supplies specify a minimum current (or maximum load resistance) to maintain stability, while sensors, opamps, and DACs have a minimum output impedance (or maximum current) required to maintain accuracy. The way I'm reading it,his one seems to be backwards to the convention.
It's interesting that they claim an operating current of 200uA when their minimum load draws 500uA at 3V3. Perhaps this value doesn't include the output current, or a marketer is specifying the device at 0% humidity and 0V out?
In the end, the only way to really know is to call Honeywell and ask for clarification, or to attach the output to an oscilloscope and pot and see whether it's both stable and accurate at various impedances below, at, and above 65k.