Alles Gute,
When the comparator output is in the "0" state, the pull-down transistor is on, and presents a very low impedance to the outside world. For an open collector (drain) comparator in the "1" state, the impedance presented to the outside world is the pullup resistance. Capacitively coupled noise "sees" this impedance. So the lower the pullup resistance, the more attenuation the capacitively coupled noise will see, and the less susceptible the output will be to capacitively coupled noise.
Regards,
Kral