I could be wrong (since article is paywalled) but as a DApp dev, Proton probably has a wallet with enough Monero to run this smart contract without anyone needing to add any money at all. So you wouldn’t be getting a Monero wallet in it. It would simply mint an NFT that you could then refer back to for verification that this is the same address that I say it is. It would simply leverage the monero chain every time an account was created and mint that as a unique ID (NFT!).