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The two 10Hz sections have an opamp in between, so that they will overlap and make a 2-pole 10Hz filter.
The opamp has a high input impedance, therefore it can have a higher input resistor, like the 16.2kohm resistor. It is better to have higher resistors than higher capacitors, due to the cost and size of the later.
The second filter is a different story. First, your diagram says that the circuit can feed up to 1000 (!) ADCs. Well, even if they are not 1000, still, a large number of ADCs will draw a combined current which will create a voltage drop on the second filter resistor. You want that resistor to be as small as possible, so that the voltage drop on it is small. The drawback is that now you need to increase the cap 100 times.
Moreover, most ADCs need to have a small source impedance in their input. This is due to the ADC analog input structure, which is usually a sampling circuit, and a large source impedance significantly affects the ADC performance.
The guy that designed it wanted to have as little noise as possible on the ADC reference input. An ADC measurement precision is as good as the reference voltage, besides some other things like linearity and drift. So, the more filtering on the reference voltage, the better. This has nothing to do with the ADC sampling rate capability.
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