You probably haven’t changed the display name, which is probably what is being displayed. “nicename” is used for the author’s posts page url and not for display.
UPDATE wp_users SET display_name = replace(display_name, @old_user, @new_user);
You probably haven’t changed the display name, which is probably what is being displayed. “nicename” is used for the author’s posts page url and not for display.
UPDATE wp_users SET display_name = replace(display_name, @old_user, @new_user);