> Interop 2022 has ten new focus areas:
> There are also five additional areas that have been adopted from Google and Microsoft’s “Compat 2021” effort:
> A browser’s test pass rate in each area contributes 6% — totaling at 90% for fifteen areas — of their score of Interop 2022.
> We believe these are areas where the standards are in good shape for implementation, and where improving interoperability will directly improve the lives of developers and end users.
A "test pass" could just be a test on which all three browsers give exactly the same result. But that would immediately imply that all three browsers would have the same Interop score, which isn't true. So I would guess that the number refers to "compliance with a standard", where you can be objectively right or wrong, rather than strictly to "interoperability", where all that matters is whether you agree with everyone else.
(The other 10% of the score really does appear to be graded on interoperability:
> Interop 2022 has three investigate areas:
> These are areas in which we often see complaints from end users, or reports of site breakage, but where the path toward solving the issues isn’t clear. Collaboration between vendors is essential to working out how to fix these problem areas, and we believe that Interop 2022 is a unique opportunity to make progress on historically neglected areas of the web platform.
> The overall progress in this area will contribute 10% to the overall score of Interop 2022. This score will be the same across all browsers. This reflects the fact that progress on the web platform requires browsers to collaborate on new or updated web standards and accompanying tests)