I agree that that is what the author intended to communicate. But I actually think that's a bigger stretch than my own interpretation - it changes how the information was determined, which has a definite impact on the outcome.

The reason why I posted was to suggest that the author should have worded it the second way, i.e.

A man has two children, and one is a son born on a Tuesday. What is the probability that the other child is also a son?

Which leaves no doubt. I guess I didn't really make that clear enough with my original post.