Oh, sorry, my answer totally did not address your question, I didn't see the top level question.

No, coinjoin has nothing to do with cashu.

This is a LN address server, which when it gets called fetches an invoice from a cashu mint, as soon as it gets paid, the mint issues new ecash tokens (nuts), sends them to the LN address server, who then forwards them to the npub that was in the address.