Context matters and in context the term is decidedly male. The article Wikipedia credits with coining the term has this to say:

> The Berniebro is not every Bernie Sanders supporter. Sanders’s support skews young, but not particularly male. The Berniebro is male, though. Very male.

> The Berniebro is someone you may only have encountered if you’re somewhat similar to him: white; well-educated; middle-class (or, delicately, “upper middle-class”); and aware of NPR podcasts and jangly bearded bands.

Source: https://www.theatlantic.com/politics/archive/2015/10/here-co...