But, isn't the blind output known by the coordinator according to the github link?
Sorry, I am not sure what you mean. From the github link you provided the process of CoinJoin consists of four steps:
Simplified workflow:
1. User provides its input and a blinded output to the Tumbler.
2. Tumbler signs the blinded output and gives it back to the User.
3. User unblinds the signed blinded output and provides the server the signed output through a different anonymity network identity.
4. The Tumbler constructs the CoinJoin transaction and gives out to the Users for signing.
Please pay attention to the highlighted part. That means you register your inputs and blind outputs with one Tor identity, but your unblinded outputs with another Tor identity.