That's fair I suppose, to me, "bro" is an inherently gender neutral term, though "girls" is gender neutral to me in the same vein.

Adding on the 'gender neutral' is kinda redundant, and I can see why it would be annoying, actually, it's annoying me too now, because if the writer simply used "bros" and not "bros (gender neutral)", the expression's gender (gender/non-gendered) would not have been moved to gendered, and most people would understand it to be a gender neutral expression.