It's simply that they took an anecdote and came to a really general conclusion about how good one gender was.

They were talking 'as if it were inherent', as if when things were liberalised women would still be more productive than men in that particular class.

Is it true?

Probably not since any greater achievement is due to that women currently must work harder simply to be seen as equal. If the social situation is normalised, women won't simply work harder than men because they are "the productive half of the population".