I don't think the brown is smaller than the black one. Look how the top and down tube are spaced on the headtube.
( Never trust sellers with sizing accurately ), and i think the black is better specced anyway.
Looking at the head tube junction, I think the black one is actually smaller - the top and down tube are basically touching, while on the red/brown one, there’s a couple cm gap.
I don't think the brown is smaller than the black one. Look how the top and down tube are spaced on the headtube.
( Never trust sellers with sizing accurately ), and i think the black is better specced anyway.