You just did not approach this constructively. It would have been better if you asked first about how the impact was and could have be measured. Or at least responded more directly when they tried to explain the impact better. Instead of making and sticking to an assumption that the service wasn't useful.
It may well be that the person misunderstood their impact, but your arguments did not address that after the person came back with theirs. They could have been an edge case, that they are in an unfortunate situation in the human process of deciding rewards, where choosing and calculating metrics is itself subject to errors in judgment, and you tried to generalize your experiences to their corner of the world, which normally requires a stronger questioning.