[ilyt]

Reaction time is time to react to (randomly generated) stimulus. So it measures the delay of our inputs, and delay of our outputs.

You are not reacting to stimulus. You are producing event (keypress) and waiting to see result.

Brain sends the message, it hits the fingers some miliseconds later but brain already knows what to expect and is already watching. So the net effect is "okay I knew I pressed the key, why nothing changed?"