I mean, there are just 168h in every week and I sleep about 70 of them. I could probably go with 60 if I wanted, but that still just leaves ~1h per day for non-work related tasks.
Maybe these people are counting their breaks and when they're sitting on the toilet thinking about a problem. If this is the case, I would get to >80h work a week too.
It works like this: they are always working.
Basically anything they do that is not 'work' is a 'break'.
So food, gym, maybe watching a film. That's literally in their view a 'break' from working.
I know people like this - and I go into this mode myself sometimes.
Your default behaviour is to be 'working'. That's what waking hours are for.
Mind you 'reading HN' probably counts basically as 'work' in their minds, similarly reading the news.
But this also covers the hours I'm laying in bed and try to fall asleep.