Ironically, none of this has intrinsically to do with his not liking to program on Saturdays, yet ends up reinforcing the notion that, for whatever reason, there is a correlation.
I know at least five guys who have small children and hack in their spare time. Yes, it's a struggle, but they all do it. I also know quite a few with small children who never do that. They never did before they had kids, either, but the kids furnish a nice excuse. Kids are handy that way. (Edit: notice how the author plays this card, even though he already said he almost never programmed outside of work or class.) Anyway, my point is that the first group are really good programmers and the second are, by and large, not. Anecodotal though this may be, I buy the idea of a correlation.
P.S. Another trait that good programmers tend to have is not seeing themselves as good enough and not getting defensive about proving how good they are. Exercise to the reader.