The answer? Women aren't "hardwired" to be as good at the game as men. His evidence? Short pointed out that of the top 100 chessplayers in the world, 98 of them are men. And the brains of men and women are different. Therefore, women are weaker at chess.
It doesn't follow from Short's evidence that biological differences in brains between the sexes is the reason women are weaker at chess. That's merely an observation, not proof. The often-cited reason for women's absence in the game is cultural:
Sabrina Chevannes, a British International Master said:
“Unfortunately, I do think there is a lot of sexism at every level of chess, from beginners right the way up to the top. We have to admit that it’s there. It has been been present throughout my entire chess career and will be present for years to come. Nigel’s views are pretty representative of most of the men who are competing in chess.
Certainly it's easier to make a case for sexism as the reason women stay away, rather than differences in the brain.
The odd thing about Short is he believes he's proved something rather than making an observation that may or may not have anything at all to do with the differences in skill levels of men and women in chess.
School textbooks post-Short: "Women are inferior to men in chess because they aren't hardwired for the game as men are." It's a joke, but Short is serious.
For a few more examples of Short spouting silly things, check the "Controversies" section of his Wikipedia page.