The maintainers of the PEP8 tool decide what goes into it.
As you noticed, these do not always match the PEP8 style guide exactly. In this particular case, I don't know whether it's an oversite by the maintainers, or a deliberate decision. You'd have to ask them to find out, or you might find the answer in the commit history.
Guido recently asked the maintainers of pep8 and pep257 tools to rename them, to avoid this confusion.