When the user-config.py doesn't exist, pwb.py starts generate_user_files.py but passes all arguments except the first one. So if someone executes python pwb.py login pwb.py will pass login as an argument and generate_user_files.py complains accordingly:
python pwb.py login NOTE: 'user-config.py' was not found! Please follow the prompts to create it: WARNING: Running on Windows and transliteration_target is not set. Please see https://www.mediawiki.org/wiki/Special:MyLanguage/Manual:Pywikibot/Windows Unknown arguments: login