Non-binary genders are not automatically trans.
Cisfem non-binary, cismasc non-binary, cisandrogynous, cisneutral, cisnull, cisgenderless, cisxenine, cisoutherine, cisaporine, cismultigender, cismulti, and cisunlabeled people exist.
This could be due to being intersex and raised with multiple socially imposed genders, or an unclear socially imposed gender.
This could be due to being socially imposed as a cultural gender that does not fall into the Western binary.
This could be due to being plural, and having formed in the innerworld with a non-binary gender that has been present from the very start, having never experienced any socially imposed gender and thus feeling as though no transition ever occured.
This could be due to so many things.
Yes, non-binary people are often transgender or cistrans.
But they can be just cisgender, too.