This makes it difficult to compare resolution differences between the One X and the Pro because limiting scaling to the horizontal dimension introduces subtle artifacts in addition to changing the clarity and detail in an image.
It holds the vertical dimension constant at 2160p and only varies the pixel count on the horizontal dimension. Dynamic scaling typically decreases the number of pixels on both the horizontal (3840P) and vertical (2160p) dimensions in order to preserve other features such as frame rate.
Native 4K resolution puts 3840 x 2160 pixels on the screen and is often referred to as 2160p. World War II makes use of dynamic resolution scaling on both the One X and the Pro.
Note the difference in detail on the packs between the One X on the right and the Pro on the left.