Exactly. I mean, it's not like it's a sci-fi show with infinite diversity in infinite combinations. Astonishing how some forum users have real issues with this when it pops up.Why wouldn't an entire species be non-binary? We've had an entire species be androginous before.
We have plenty of evolved vertebrates here on Earth that are either sequentially or simultaneously hermaphroditic. Clownfish. Beardies. Parthenogenetic (sic?) etc - some snakes, hammerhead sharks. Not a big leap to assume physical evolution (which we've seen portrayed as containing similar classes then orders of animal life on Minshara class planets) might have deviated in other worlds, and neurology, psychology and identity etc matched up to dovetail this.
There's no reason why future depicted species (humanoid or not) need to all be of 2 genders. We've seen three genders (although the catalytic third gender trope) in Star Trek already.