I'd say it's not nearly that unlikely. If you're smart, you have a good idea, and you work hard on it, your chances of that kind of success (and we're only talking the $10 million payday here, not the $billion payday) are something on the order of one third.
What I'm more concerned about is the fact that the guy said he tried a four-hour workweek but got bored, and now he wants to work 100-hour weeks so he can retire in seven years. What does he think he's going to do when he retires?
$10m company payday, or $10m personal payday? If you're looking for a $10m personal payday, your company needs to be brought at for quite a bit more (depending on number of founders and investors), so if we consider the set of smart, hardworking people, the percentage of those that sell their company for $50-100m is substantially less than 30%.
Now, if you and the author are talking about $10m company payday (lets say $1-2m for yourself), that's about a decade or two of decent income (ie, not enough to retire) and as you mentioned, what would someone used to working 100hr weeks and labeling relationships as "distractions" do with their time? I'm really failing to see the author's point to all this.
What does he think he's going to do when he retires?
He's going to work 85-hour weeks, of course!
One major theme of The Four-Hour Workweek is that, for many people, it takes practice and training to do less work. You get habituated to the stress and the pressure, such that life without it begins to feel wrong. You need to train up the areas of your life that fall outside of your career, or they'll atrophy, and you won't be able to stop working because your mind and body will rebel.
Then you'll be forced to find something else to do. You can't watch TV 80 hours a week for a year - you'll go crazy. But you can watch 4 TV hours a day, every day, for the entire duration of your life. That is 28 hours a week. Or 1 year in 4.
Probably the guy will take a break for 6 months after/when he succeeds, then do it all over again. Or he'll start doing something else obsessively. Either way he's not going to be bored.
What I'm more concerned about is the fact that the guy said he tried a four-hour workweek but got bored, and now he wants to work 100-hour weeks so he can retire in seven years. What does he think he's going to do when he retires?