... doesn't mean they need to deal exclusively with binaries.
TFA alludes to this issue with the "gallery of misidentifications", but doesn't get as far as asking surely the most important question: what exactly does this software claim to determine? It's clearly not "biological sex", because you can't determine that from a photo (even a full-body naked photo) -- what about the 1% of people who are born intersex? And it's definitely, definitely not gender, which you could only ascertain by asking that individual.
Whilst one potential application mentioned (analysing crowds for marketing purposes) seems vaguely sensible, any system using photos to try and identify an individual's gender is reactionary, oppressive and doomed to failure.