I think it’s because nostr:npub18m76awca3y37hkvuneavuw6pjj4525fw90necxmadrvjg0sdy6qsngq955 is purple, and nostr:npub1cj8znuztfqkvq89pl8hceph0svvvqk0qay6nydgk9uyq7fhpfsgsqwrz4u ‘s purple ostrich (nostrich) became the unofficial Nostr mascot.