Paul Atreides revelation of Arrakis real name in Dune: Part Two is treated as a huge moment that proves his clairvoyance, but hes not actually the first character to call the planet Dune. After Dune: Part One laid all the groundwork, Dune: Part Two provided all the payoffs. Paul started living up to the Lisan al-Gaib prophecy, with some fervent followers falling in line and others questioning his leadership, and the Fremen waged all-out war against the forces of House Harkonnen.

https://screenrant.com/dune-part-2-movie-paul-arrakis-name-plothole/