I do believe an apology was fully in order, but the apology he gave is good imo. It includes specifying exactly what was wrong and the action he took to rectify the problem. I am indeed a very biased (in the info sense, not the Kpop sense) fan of BTS, but I am also very serious about anti-fascism and I am satisfied with his apology.
its genuinely a really good apology, he doesnt give excuses he admits to his carelessness, and he directly addresses that what he did had the potential to disappoint and hurt people. i wasnt even aware he wore the hat until i read the apology, i was amazed at how promptly he recognized and addressed the issue.