I agree with you on this, and I feel like I must be missing out on some feature of "stubs" or working with a different definition of what a "stub" is - testing

I agree with you on this, and I feel like I must be missing out on some feature of "stubs" or working with a different definition of what a "stub" is - testing with a stub implementation of the collaborator, which you have to write yourself anyway, seems to tie your test to not just the implementation of the class-under-test but also to the stub you've written. In the OP's article, I don't see the difference between what the author is calling "mock" or "stub", only that in the latter the expected value of the arguments passed to the collaborator's method are not asserted. This still seems like a mock to me.