Edit: I'm genuinely shocked by the number of comments that contain a latent sexist pretext. Maybe I've been brought up in an overly liberal environment, but I find it pretty horrendous nevertheless.
So, here's the thing. I actually consider myself a feminist. I've been outspoken in the past on things like believing that the gender gap in computer science and IT is primarily a consequence of social conditioning and that people should be evaluated and valued within an organization based on their qualifications and not based on their gender.
As such, I'm a bit uneasy with the premise of the article -- that work environments can and should be made more "girl friendly" (insofar as that goes beyond not tolerating overt sexism). But that premise came from the article, not from me. Personally, I'm conflicted there and could argue both sides. But, if we run with that premise, and try to answer the question in the title, I find it an impressive stretch to read sexism into saying, "I find mixed gender work environments more pleasant than single-gender environments."
The goal is to get the most productivity from the team/group. Sometimes that means hiring for attitude over aptitude or ...oh yes, diversity - be it race, gender, degree, life experiences, etc.