This happens pretty often in the Python world. There's a bit of an unwritten rule to leave implementation details public that would be private in other languages. Many libraries simply don't bother with prefixing privates with '_' and just leave things undocumented that you probably shouldn't touch/use.

One notable example is importing libraries in your code automatically exposes them to the caller.

    $ cat lib.py
    import re
    
    def somefunc():
        pass

    $ python
    >>> import lib
    >>> lib.re
    <module 're' from '/usr/lib/python2.7/re.pyc'>

Many packages also do `import *` from files which polutes the package namespace with all kinds of stuff you really don't want in there. For example, the popular Requests package:

    >>> import requests
    >>> requests.logging
    <module 'logging' from '/usr/lib/python2.7/logging/__init__.pyc'>

The logging module is not a public part of requests' API. It's just there because requests uses it internally.

So to answer your question, I'd say it's just common practice. If it's undocumented in Python, you should pretend it doesn't exist.