Yeah, I was very confused what exactly the "paradox" was at first, too, and why the expected interpretation should be the one it was. Here's how I finally see it:
If I say, "I have two cars, one's a 1994 Porsche 911", then I think it's reasonable to interpret that statement to mean the other car is not also a '1994 Porsche 911', but doesn't speak at all to its Porsche-ness, 1994-ness, or 911-ness. Rather, I'm wrapping them all up in a package, and saying the other is not this exact combination of characteristics.
Similarly, if I say, "I have two children. One's a son born on Tuesday," I think I now understand that I'd probably interpret that to mean the other child is not a son born on Tuesday. It doesn't speak to the gender or day of birth beyond that.
With that knowledge, that the other child is not a (son AND Tuesday-born), that's when the 13/27 arises.
If I say, "I have two cars, one's a 1994 Porsche 911", then I think it's reasonable to interpret that statement to mean the other car is not also a '1994 Porsche 911', but doesn't speak at all to its Porsche-ness, 1994-ness, or 911-ness. Rather, I'm wrapping them all up in a package, and saying the other is not this exact combination of characteristics.
Similarly, if I say, "I have two children. One's a son born on Tuesday," I think I now understand that I'd probably interpret that to mean the other child is not a son born on Tuesday. It doesn't speak to the gender or day of birth beyond that.
With that knowledge, that the other child is not a (son AND Tuesday-born), that's when the 13/27 arises.