The article states that he appears (in some places) to have two X chromosomes; and that if this were true, he would be a woman. That's not strictly true: it's possible to have two X chromosomes and one Y, a condition known as being XXY or having Kleinefelter's Syndrome.

Individuals with Kleinefelter's Syndrome appear male, and the condition may go unnoticed. Most are sterile, but not all.

I'm not saying Watson is XXY, mind you. I'm just saying that with roughly 1 in 500 males having an extra X chromosome (according to NIH), then this is not in itself a reason to discard the data. It's similar to the fact that he has two sons: that strongly suggests that he was fertile, but it only proves that his wife was.