Just because some identity is contradictory to you doesn't mean it can't make sense. Actually, nuanced identities are often contradictory when you know the basics of it, ignoring all details and complexity a multilabeled or combined identity can be.
If you think cisgender nonbinary people can't have a definition bc then it would describe someone who is not cis, then you're in the wrong bc just cause something describes you it doesn't mean it applies or include you bc the identity requires self-identification as well.
Same goes for bi lesbian, demisexual, or lesboy, you 'are technically lesboy' (/demi/lunian) but refuses to label yourself as such? Cool then you're not/don't experience that identity 🤯 and that's okay. But to imply anyone with such identity are not that thing bc it can't exist, then you're being a reality denier, bc ppl with such identities exist regardless if you recognize them or not. For instance, just bc someone uses ungrammatical conlangs doesn't mean that language can't exist. In fact, it's written already and it's on you if you're gonna cry or ignore.
Also transhet people are allowed to be nonbinary; binaryn't transfems/transmascs are allowed to be hetero due to their alignment, presentation, AGAB, or any other typical reason.