FWIW, knocking on the door of 40 my RHR is about 56bpm, max around 190-195bpm, mean over a purposefully super- slow recovery ride around 100bpm, a relaxed ride around 120-125bpm, an intense ride 150-160bpm with balls-out hill efforts maxing out at 185-195bpm.
As others have said 120bpm is the opposite end of the scale to a full effort and what, barely zone 2 for most people?
Sounds like the man in question doesn't know the meaning of "a big effort" and presumably you've been attacked on FB by his group of sycophants because they'd rather protect his ego from the truth of the matter. Can't stand FB groups personally; seem like a flypaper for idiots and trolls IME. Get him to join a proper cycling forum