Wiki: A Zero Knowledge Proof is a method by which one party (the prover) can prove to another party (the verifier) that they know a value x, without conveying any information beyond this point.
This is a rendition of Wigner's Friend (SP*). I don't want to discuss it too much because I'm very bias in the interpretations.
To answer your question; No idea, but could be considered either. They share information, which means it's not "Zero Knowledge" they know that the other side has computed the equation. They share that information, but compute without sharing information or formulas.
You tell me you've measured something. I say ok, and measure something myself. We tell each other we both measured something until we arrive at different measurements. In QM, it's related to spin and superposition. When we get different results "reality splits" - when we get the same result, "realities merge" - more or less.