The pre-compressed and compressed versions were loudness matched to be the same overall loudness, according to the description. My guess is that they set the compressor to actually make the waveform spikier, without fully understanding what’s going on. Just a guess, though. I can’t check to find out.
It's already known that hearing damage is cumulative, longer exposure to loudness is bad, so it seems like a common sense result in line with all existing research.