If the spec is open source, how can you say all the clients are open source? Or do you simply mean there are open source clients one can inspect and use?
There is a specification of the protocol, which is open source: https://github.com/ethereum/consensus-specs
And there are over 5 interoperable, independent and open source implementations of said specification:
- https://github.com/sigp/lighthouse/
- https://github.com/ChainSafe/lodestar
- https://github.com/status-im/nimbus-eth2
- https://github.com/prysmaticlabs/prysm
- https://github.com/ConsenSys/teku
- https://github.com/sifraitech/grandine
...
Furthermore, it's implemented and running. You could argue that someone in particular has made a poor or incomplete explanation of how it works but not that they way it works is unfathomable or being patched as your speak. It's already implemented, go look at the code if you don't want to believe what anyone says.