Further in the article he goes over exactly why he feels that its allowed to both test a single classe or multiple at once, going as far to give a name to them: solitary vs sociable unit tests.

Then, he goes on to, and let me emphasize this, defend the criticism that other people make that this type of test is not a unit test. (sound familiar?):

Indeed using sociable unit tests was one of the reasons we were criticized for our use of the term "unit testing". I think that the term "unit testing" is appropriate because these tests are tests of the behavior of a single unit. We write the tests assuming everything other than that unit is working correctly.

I'm not sure how thoroughly you're looking to be refuted here but I feel I can't quite do a better job.