If the only indicator that these employees "needed" to go was the simulated keyboard activity then either:
a) the employees met all required KPIs and delivered well and were just meeting some dumb policy while actually being totally fine, and therefore shouldn't have been fired; or
b) the company has literally no way to tell if someone is actually useful and many of the people not using such devices could easily be far worse performaers.
In either case, firing someone based on this sort of monitoring or information should be illegal.
a) the employees met all required KPIs and delivered well and were just meeting some dumb policy while actually being totally fine, and therefore shouldn't have been fired; or
b) the company has literally no way to tell if someone is actually useful and many of the people not using such devices could easily be far worse performaers.
In either case, firing someone based on this sort of monitoring or information should be illegal.