Avira- not a contradiction. Yes he needs to fulfill all his Halachic criteria to get geula set up. But once that’s done, why is he called a king? What’s the significance? The answer is that he will elevate the people by being משכמו ולמעלה מכל העם in his Neshamas level and comprehension of Elokus, which he will then use to elevate the people. (He won’t need to force/ control the people because we won’t need policemen when moshiach comes. So this is the loftier idea of a king.)
See Derech Mitzvosecha- minui melech for more