Minnieee33:
It's not really the CP ship. It was how he acted so rude toward a coworker and how he answered his question. Everyone gave a speech about their character as their final speech but he just said SF is gone but CY is here. This was a fan event for the drama, not a CY fan event. This is the main reason people are mad.
Fans of the drama are hurt by his action. As this is not related to Crystal, he acted on his own.
There was a meeting before with the head of the company (who was also at the event and appears in the video), he was there as a spy. (Yes, his way was cold, he didn't know how to act). But you must understand his situation. (He was sad, pressured, unnatural. He had a right to have a normal closure in the drama, and he was not allowed.) They left him so scared, rebuked him so severely, that the result was this.