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The Heroku Django tutorial app uses gunicorn as the server, as you can see here:
https://github.com/heroku/python-getting-started/blob/master/Procfile
There is no special gunicorn config in the tutorial app, so you are running with gunicorn default settings. You can see what they are here:
http://docs.gunicorn.org/en/stable/settings.html#worker-processes
You’ll note that this means you have a single worker process, of the sync type (i.e. no greenlets magic to enable concurrency within the single Python process)
It does say you can scale gunicorn to use multiple processes (still on a single Heroku dyno) by setting the WEB_CONCURRENCY environment variable, on Heroku this is easily done from your local shell using the cli tools:
$ heroku config:set WEB_CONCURRENCY=4
Gunicorn docs suggest setting this to “A positive integer generally in the 2-4 x $(NUM_CORES) range.” Your basic Heroku dyno will be a single core.