I think it's because female characters in bl normally have some sort of connection with the seme, and are supposed to appear more dominant than the uke, like a threat.
That was strange because I thought the first guy was the prot but then he isn't... but I was mentally prepared for him to be and then he wasn't and I felt weird...
Finally a yaoi that's not so stereotypical, a reversal, that doesn't promote gender stereotypes