The reason why Harumafuji was in the wrong is because he was overreaching his station. Beating someone for disrespect is expected to be done by the stablemaster. By doing it himself, Harumafuji was interfering with the stablemaster's authority and severely disrespecting the stablemaster. Takanohana was completely in the right to be offended over that level of disrespect. Isegahama should have beaten Harumafuji himself to atone for that.