Wait, they thought Kizaru was bleeding there?
How can one miss the point so badly? Kizaru was flexing his defense there, showing to Sentoumaru that even landing a clean hit is pointless. That's why he's scrathless in the following panels.
Oda sometimes draw these inked particles (which I guess are confused for blood in this case) during fights, we had the same for Luffy vs Kaido act 1 although Luffy was literally unable to hurt Kaido pre ACOA.