The "Discover pull requests from forks" allows to set a trust level. The trust level "Contributors" is ambiguous, since it does not refer to all contributors, but actually only to collaborators (in the GitHub definition of collaborators => https://developer.github.com/v3/repos/collaborators/ ). Since GitHub collaborators have to be explicitly added to a repo, this is usually a smaller group of people.

This ambiguity is somewhat explained in the info/help text (when you click on the icon left of the trust drop-down menu), but I'd recommend to make it clearer by renaming the entry in the drop-down to "Collaborator" or even "GitHub Collaborator". I don't see a value in using a different term for it.

Actual examples of misunderstanding:

https://bugs.eclipse.org/bugs/show_bug.cgi?id=549571

https://bugs.eclipse.org/bugs/show_bug.cgi?id=550512#c12