A finger-tapping test is often used to normalize other kinds of response time, essentially to control for uninteresting between-person differences in neuro-muscular performance. Was there some kind of cognitive control task too, e.g. where they ask you to refrain from responding to certain stimuli? Typically in something like that you'd have a hard and an easy condition, and the difference in average response times between those conditions is a proxy for "cognitive control" or impulsivity. If an employer were interested in that they'd want to remove the effect of finger speed.

I don't think companies should be administering psychometric tests. But it doesn't make the task you refused to do meaningless.