I am skeptical of the link entirely. It says gevent does not support Python 3, yet if you look at the PyPI page [0], it says "Gevent runs on Python >= 2.6, Python >= 3.3, or PyPy >= 4.0.1 (but not PyPy3)". Is the lack of PyPy3 really worth saying Gevent doesn't run on Python 3 (the language, not CPython specifically)? Perhaps this website is out-of-date in some respects, and helps contribute to the confusion.
On an unrelated note, a lot of people I have encountered claim Gevent as the reason they haven't switched yet. For now I guess such claims are shaky, assuming the PyPI page isn't false advertising.