It's certainly reasonable for a studies across fields with hourly pay or, e.g., including both part-time and full-time (such as the BLS survey cited by the Forbes article), but I'm not sure we can make that assumption for software development - programmer productivity in a given time period is, on its own, somewhat mythically considered to vary by orders of magnitude.

Fair point.

I'd argue it's a more logical and likely explanation than sexism though.

Anecdotal evidence matches this up pretty closely. Better programmers tend to work more, it's just a fact of life.