It doesn't. It was intended to be bigender. If you'd know the story and the characters well you'd know it was used in the correct way.
It kind look like it was referencing bisexuality though....
No, not at all. Don't you know how Suzuki acts around Sugiki? In a really feminin way.
His feminity didn't come naturally though. He had to be trained to take on the female role. Check out chapter 4. Knowing this and having trained him....why would he question his gender? Plus in previous panels he mentioned him "swinging both ways" which alludes to bisexuality. You don't need female characteristics to be with a men and he knows better than anyone that he had to adapt those female characteristics his dancer to allow others to take the lead. It seems like you are pushing gender. Even in her reply to him, "there's no way he would go for a guy," suggests bisexuality.
I also think it was a translation error. The question is not about his identity as male or not-male, but rather if he is usually attracted to men. Thus, bisexual.
It's not an error. This was already backed up by multiple people who speak japanese very well and have seen the raws and are familiar with those terms. The question is not about if he is usually attracted to males. Sugiki feels feminine vibes coming from Suzuki quite often. Also, he already asked Aki if Suzuki was bisexual and she said no. No point of asking it again.
Thank you.
Bisexuality =/= Gay =/= Bigender
why does this mashup of things always pop up