I just realized something, Kuzan could have coated his fist with coc later. This panel is just to show “ice glove”, notice how there’s no hardening here.
Observe the actual panel before the clash, we see neither Garp nor Kuzan’s hands. In the actual clash, Kuzan now has armament haki so it’s clear that he first coated his fist with ice then he coated it with haki. So the panel with “ice glove” doesn’t actually prove that Kuzan didn’t coat himself with coc.
Chronology: Kuzan uses ice glove —> Kuzan coats his fist with haki (we don’t see this) —> punch Garp’s face