Per docs it should default to DEBUG. I'm not sure if this is django's fault that it isn't explicitly set somehow, or the plugin's fault that it assumes False.
In any case, if I'm not mistaken, it can be fixed by changing:
if not template_settings.get('OPTIONS', {}).get('debug', False)
to:
if not template_settings.get('OPTIONS', {}).get('debug', settings.DEBUG)
If DEBUG happens to not be in the user's settings file, settings.DEBUG defaults to False, which seems sensible to me.