This is the context: https://github.com/js-cookie/js-cookie/issues/286
Here's the e-mail response from support dates from Apr 3, 5:19 AM PDT:
The build status matrix shows you the status of the most recent build for the specified Sauce Labs username. From the Sauce side of things, we don't know whether the latest build for the user js-cookie relates to the master branch, or a PR or anything else. If the failing tests for a PR are run by the same Sauce Labs account, js-cookie, and that's the most recent build run by that account, that's what the build status matrix will show.
Later in the same e-mail:
I can't say that I've heard of this use-case before and to the best of my memory, I don't believe the browser matrix has functionality that can filter out the builds that come from the master branch and not the ones that come from Pull Requests, especially if all the tests are using the same Sauce Username.
The idea here is to allow the Browser Matrix to show only builds run on master. I believe that's reasonable, given that one would want to show the passing browsers in the README to prove the system is working, and a failing test from a Pull Request will be a false positive (the failure is in the PR, not the master branch, therefore it's not the project that is failing, and that's exactly what it looks like).