It’s true that films of the time were finished in 2K, but in order to make sure all the detail is gained from a film print, it is often scanned in 4K or higher. It’s basically like the detail of the 2K master is ‘scattered’ across the fine grain of the film, which is in danger of sometimes being lost in the grain structure unless it is scanned in sufficient detail to retrieve it. I hope that this isn’t more confusing, it’s just difficult to describe without viewing 2K vs 4K film scans.