I don’t understand how people are so pervasively misreading this.
The key word there is ‘always’. I think that few proponents of cultural appropriation discourse would argue that a writer from one particular cultural identity can never write a character from another background. Rather, they would like writers to take on that challenge in a responsible way.
Its almost as though privileged groups are so unfamiliar with the experience of oppression that they confuse it with legitimate criticism (typically from groups who actually do experience oppression).