Wow, this is great news!
For one thing, it should now be possible to comment on their statements and things, using a fediverse account. Look at that, public institutions open to communicating with anyone, no longer limited to Twitter/Facebook users. 
Also, this should help more people learn that alternatives exist:
The two platforms are part of decentralised, free and open-source social media networks that connect users in a privacy-oriented environment, based on Mastodon and PeerTube software. By launching the pilot phase of EU Voice and EU Video , the EDPS aims to contribute to the European Union’s strategy for data and digital sovereignty to foster Europe’s independence in the digital world.
EU working towards digital sovereignty using free and open-source software. They even use the word “free”. 