If a man leaves you on the ground unconscious and ignores you (which Luffy did to Kizaru twice), you lost the fight, even if you get up again and can fight later.
This plays directly into Kizaru’s choice to feed Luffy. He knows while he was laying there after Luffy’s fist went through his head, Luffy could have rushed him and killed him while he couldn’t move. Instead he simply moved on with no ill will or violent intentions towards Kizaru at all. Kizaru knows what kind of person he’s fighting and the kind of people he’s fighting for, and he makes a choice to give Luffy the same treatment.