That's the bone of contention here. Nobody is keeping women out of computer science; they're largely just preferring not to enter the field. The point of the article, echoed by many commentators over the past few years, is that it's a "problem" that women are largely staying out of computer science.
If you believe in the blank slate theory of human nature, of course it's a problem, because under this worldview, women's default preferences are the same as that of men, so some external factor must be pushing them away from computer science. The teach for this factor has become increasingly desperate the past few years: now we're down to Star Wars posters.
I believe it's more parsimonious to reject the blank slate theory and understand the world through the lens of innate differences in life preferences between genders, and that it's this innate difference that leads to different gender balances in various fields.