Easy - choose a domain where pre-knowledge is gender-biased: "Design a web application to manage a fantasy football league", "Implement a D&D character generator", "Implement an optimal queueing strategy to solve the urinal-allocation problem (http://blog.xkcd.com/2009/09/02/urinal-protocol-vulnerabilit... ).
Not suggesting that's what fogcreek do, of course, but just to demonstrate that a coding test could easily have a gender bias - or a cultural one, for that matter.
If a person of any gender can't turn urinal allocation into selecting a subset of range(0,N) of maximal cardinality subject to the constraint that neighboring integers are excluded (assuming my quick skim of the problem didn't gloss anything over), they are a bad developer.
Lots of times you need to develop stuff without domain knowledge. My startup targets women's fashion, which I know very little about. If I were to give up or fail because the problem involves plackets and silhouettes, I'd have already quit and gone back to NJ.
Xkcd is wrong about that as it depends whether the man is a huncher or an arcer. I suppose you're right, only a man would know that. But Joel is well known for Fizzbuzz.
Not suggesting that's what fogcreek do, of course, but just to demonstrate that a coding test could easily have a gender bias - or a cultural one, for that matter.