I think the point is that it depends on what prompt the man is implicitly answering. If you ask parents of two children if they have a boy 3/4 of them will say

I think the point is that it depends on what prompt the man is implicitly answering. If you ask parents of two children if they have a boy 3/4 of them will say they do, but if you ask the same parents to randomly name the gender of one of their children 1/2 of them will say they have a boy. Those two different scenarios lead to the 1/3 and 1/2 odds respectively.