There is no universally accepted definition of poetry, and some say it can’t be defined. However, poetry is generally considered to be writing that follows a defined structure (for example, the rhyming lines of traditional verse) and that uses rhythm or rhetorical devices, such as figurative language or allusion, to add beauty and enhance the meaning of the text. It is language with a perceived pattern that is appreciated as art.
For chiastic poetry, the defined structure is the inverse ordering of parallel elements. But then it needs something more. A chiasm consisting only of inversely arranged parallel elements would be about as much a poem as a “verse” consisting only of rhyming lines. It wouldn’t be very impressive poetry. Classical chiastic poetry generally includes figurative language, allusions, or devices such as repetition to beautify and enhance the meaning of the text. But, strictly speaking, even a bare chiasm is more like a poem (from Greek poema, meaning “a thing created”) than prose (from Latin prosa, meaning “straightforward”). It isn’t “straightforward” writing, but forward and back. And it is an artistic creation.
A chiasm is a distinct element with a prescribed structure and a sort of rhyme (of meaning). It’s not the kind of poetry we are used to, but if it isn’t a poem, what is it? I don’t know a better word to describe it.