Nothing about that bike seems gender specific to me...the best I could come up with is the sibling is a man who thinks the name "Merida" sounds like a girl name or decided the top tube is too curvy and therefore resembling of the female form.

Personally, I'd probably buy a pink/yellow bike with "princess express" written on the top tube if it meant I could save $50 over an similar bike in more manly earth tones.