Current directory in Python module search path not working for django-admin

I was studying a document on Django settings. It reminds us that the settings module should be on the Python import search path. So I added the following two lines to .bashrc as suggested in here:

-dell:~/Documents/DjangoTutorial$ tail -2 ~/.bashrc
export PYTHONPATH=$HOME/Documents/DjangoTutorial/mysite
export DJANGO_SETTINGS_MODULE=mysite.settings
-dell:~/Documents/DjangoTutorial$ . ~/.bashrc

and "django-admin runserver" is working from anywhere, with sys.path in Python3.7 showing:

>>> sys.path
['', '/home/Documents/DjangoTutorial/mysite', '/usr/local/lib/python37.zip', '/usr/local/lib/python3.7', '/usr/local/lib/python3.7/lib-dynload', '/usr/local/lib/python3.7/site-packages']

Then I read article1 and article2 which imply that "sys.path" consists of : current dir.(denoted as ''), PYTHONPATH, standard and installed libraries. So I invoked django-admin strictly from the PYTHONPATH directory but commented out "#export PYTHONPATH" in ./bashrc and got an error as shown below:

-dell:~/Documents/DjangoTutorial/mysite$ django-admin runserver
Traceback (most recent call last):
...
**ModuleNotFoundError**: No module named 'mysite'

I then checked sys.path and '' was there:

-dell:~/Documents/DjangoTutorial/mysite$ python3
>>> sys.path
['', '/usr/local/lib/python37.zip', '/usr/local/lib/python3.7', '/usr/local/lib/python3.7/lib-dynload', '/usr/local/lib/python3.7/site-packages']

My question is that if '' is equal to PYTHONPATH in this case and why cannot it find the settings module?