I don't see why this is that hard to believe. 31.5 miles a day. Run 3 times a day 1 longer (14-20) 2 shorter runs (6-10).
Averaging 8 min pace = 4hrs 12 mins of running.
Averaging 7 min pace = 3hrs 40 mins of running.
Averaging 6 min pace = 3hrs 9 mins of running.
It's really not that crazy its just depends on your frame of reference and the mental framework you have.
A lot of people are discovering the norms that we call normal today are only normal because our culture accepts it as normal.
At one point in time the culture of the day thought it was physically impossible to run a 4 min mile, the world was flat, etc.
Culture norms often act like a cage that we live our life in. Cool thing is that people are learning to think outside the box and people are being adventurous and finding out a bunch of stuff we believe and accept is just loads of crap.
A friend of mine has recently started running up to 3-4 times a day and running up to 200 miles in a week. Not that I recommend it but he has found a way that works for him and he has managed to stay healthy and has made huge improvements.