nostr:npub1yzdza73gkyzkrmvlttudds3wx6fp3ca8nq3tj3w4385z44yxredse08c3r nostr:npub174t832slt4252dk526cnh64sfa3k6claah2cdl3c5n9eeeyvjz7q2fmqm6 that's a Nostr user actually. They are using Mostr to communicate with the fediverse. https://soapbox.pub/blog/mostr-fediverse-nostr-bridge/

Their handle is their Nostr public key.