He never said “only“. For his argument to be true it's enough that the features are more prevalent among young single men, and me didn't say more than that.

The work ethic in question involves “long hours and self learning“ self learning implies that it probably also happens outside work hours. People who are in a relationship are obviously less likely to work long hours and self learn in their free time.

Statistically, young people are also far more willing to do long hours.

I'm a bit torn on bringing gender into it. Women are more likely to work half time, but I would expect them to be better at predicting needs (yes, I'm aware that's potentially sexist).

So basically I find everything very reasonable if you assume he didn't mean the worst possible interpretation. I don't see the gender bias, but I'm sure there are arguments I'm not aware of.