Nothing is decided yet, according to their website:
The Eurosystem is experimenting with different approaches and technologies to making a digital euro available. This includes both centralised and decentralised solutions such as DLT. No decision has been taken yet, however.
They just have announced their plans, but its still many years away
To me fediverse just means different communties being able to talk to each other.
It seems like a lot of people use fediverse as a generic term for any decentralized system.