Tudo está bem, você pode ignorar o problema, isso é um erro. Seu comando não causou nenhum dano.
O "problema" foi este, e está tudo bem no seu caso:
softwareproperties.ppa.PPAException: 'Error reading https://launchpad.net/api/1.0/~team-xmbc: Not Found'
em:
Traceback (most recent call last):
File "/usr/bin/add-apt-repository", line 119, in <module>
shortcut = shortcut_handler(line)
File "/usr/lib/python3/dist-packages/softwareproperties/SoftwareProperties.py", line 837, in shortcut_handler
ret = factory(shortcut)
File "/usr/lib/python3/dist-packages/softwareproperties/ppa.py", line 382, in shortcut_handler
return PPAShortcutHandler(shortcut)
File "/usr/lib/python3/dist-packages/softwareproperties/ppa.py", line 346, in __init__
info = get_ppa_info(self.shortcut)
File "/usr/lib/python3/dist-packages/softwareproperties/ppa.py", line 333, in get_ppa_info
_get_suggested_ppa_message(user, ppa))
File "/usr/lib/python3/dist-packages/softwareproperties/ppa.py", line 292, in _get_suggested_ppa_message
lp_user = get_info_from_lp(LAUNCHPAD_USER_API % user)
File "/usr/lib/python3/dist-packages/softwareproperties/ppa.py", line 87, in get_info_from_lp
return _get_https_content_py3(lp_url)
File "/usr/lib/python3/dist-packages/softwareproperties/ppa.py", line 107, in _get_https_content_py3
raise PPAException("Error reading %s: %s" % (lp_url, reason), e)
softwareproperties.ppa.PPAException: 'Error reading https://launchpad.net/api/1.0/~team-xmbc: Not Found'