Terminology for antonyms can get a bit complicated, according to Kreidler in Introducing English Semantics. Binary antonyms can also be called hemispheric antonyms or complementary antonyms while non-binary antonyms may be called polar or contrary or gradable antonyms. (To complicate things further, some linguists might use "non-binary" to indicate incompatibility in incompatible antonym sets; usual examples of incompatible sets are (1) suits of cards or (2) seasons of the year.)
Having laid out this groundwork, I'm supposing you mean binary/non-binary as equated to complementary/gradable antonyms. To find the answer to your question about the antonyms contract/expand, we'll define our terms. If something can be described as binary, then that means it involves two aspects or parts: it has dual parts, not several or multiple parts.
Binary (complementary/hemispheric) antonyms are those that have no variables between them. In logic terms, if something is not Y, then it must be X. Conversely, if something is not X, then it must be Y. There are no other possibilities between. Examples: An engine is either on or off. The sky is the sky and may not be the ground, while the ground is the ground and may not be the sky; it may not even approach being the sky. You are you and not me. I am I and not you.
Conversely, non-binary (gradable/contrary/polar) antonyms are those that have variability and degrees between oppositional antonyms. In similar terms as above, for opposites A and Z, if something is not A, then it may be anything up to Z. If something is not Z, it may be anything up to A. There are many, or even infinite, possibilities between A and Z. Examples: I may be old, older or oldest. I may be young, younger or not so young. It may be hot but not too hot or getting less cold and more warm. Young/old and hot/cold are gradable antonyms and therefore non-binary antonyms, not having two exclusive parts.
Now where does contract/expand fit? Is contracting to a smaller size a one-size-fits-all prospect going from not contracted to contracted or are there grades of contraction within a broad range? The same questions apply to expansion. Is there one expansion that accommodates all? Does expansion move from not expanded to expanded with no possibilities in the middle? I think you'll see that contract/expand has many degrees for each and is therefore non-binary because there are multiple degrees to both contraction and expansion.
The logic of binary/non-binary antonyms fits very well in a truth table as one purpose of a truth table (used in math, logic and science) is to show the is/is not or true/false nature of concepts. Expanded truth tables can take into account variables and grades of possibilities. The eNotes format isn't suited to showing what a truth table would look like, but you can get good ideas of them from California State University San Bernardino (CSUSB) Web pages.