Create anime girls. Doesn't anime have boys?
According to the technical report [1], they used character portraits from Getchu [2] for training data. A cursory glance shows that the overwhelming majority of the characters are female. As a result, the characters the tool generates are likely to appear female to our eyes.
After the code is open sourced, perhaps someone should try to create make.boys.moe using character portraits from otome games [3].
[1]: 12.8 MB PDF, http://make.girls.moe/technical_report.pdf
[2]: example from report (possibly NSFW?), http://www.getchu.com/soft.phtml?id=933144
[3]: games with a female protagonist and many male characters, https://vndb.org/g542
Shit, we're over capacity, this is against fire safety regulations!
Profit.