He said he was gonna wave it off, and they tried to talk him out of it without asking why. Didn't hear them say anything specifically bad, but he flat out said he was out, and they wouldn't except it until he told the ref himself.
If he felt he was taking a beating and had no way to remedy it without risking substantial damage, it should be his right to opt out.
From the outside, it didn't appear bad enough to warrant stopping, but only he knows the reason, so if he wants out, so be it. Probably not smart for a young guy building his career, but maybe he already had a hidden concussion in training or something and was concerned.
As a fan, it sucked, but as a fighter concerned about safety, no point continuing if you know for a fact you got nothing left, or your knee is torn, or you're already concussed, etc, etc.