EUROfusion is a consortium of national fusion research institutes located in the European Union, Switzerland and Ukraine. It was established in 2014 to succeed the European Fusion Development Agreement (EFDA) as the umbrella organisation of Europe's fusion research laboratories. The consortium is currently funded by the Euratom Horizon 2020 programme. [0]
-- Wikipedia
So the reason it is called European is that it was conceived by the EU and it's partners and it primarily funded by the EU's Horizon 2020 funding programme.
[0] https://web.archive.org/web/20170830004728/http://horizon202...