Unpopular opinion.
It was all more or a grapple on the floor, I don't think there was any attempt to lead with the head, or to hit in the head. Head contact was glancing, mild and incidental.
Of course, it's also important, off the ball, and after the whistle.
With mitigation of Meafu not knowing that White had been pushed onto him, not deliberately starting something.
Calling it a headbutt is technically true, but makes it sound way worse than it was, and the degree of danger was absolutely minimal.
I'm okay with it being yellow for handbags, and let's get on with things, I'd also have been okay with it being a "harsh but fair" red. By the letter of the law, probably red, but possibly the very harshest of reds.