Clliptic lowpass filter IC
I am not sure of the exact technology used in this IC, but it is clear that it is doing discrete-time analog processing. 

As such there is no discretization of the signal level, just of the time samples. All of z-transform and discrete time methodologies apply, but considerations for the finite bandwidth and slew rate of analog components have to enter consideration. Thus the 50xNyquist requirement. 

Modern ICs that do the same type of processing are known as switched-capacitor ICs, it is possible that this one is an early adopter of that technology. 

Similar constraints also apply to chopper amplifiers. Although in their case they are better examples of modulators, of which time discretization is a special case.