Use lidar.labeler.loading.CustomPointCloudSource for your folder of .pcd files. RosbagSource is only for ROS1 bags, not extracted .pcd files.
fds = fileDatastore('your_pcd_folder', 'ReadFcn', @(x) pcread(x), 'FileExtensions', '.pcd');
source = lidar.labeler.loading.CustomPointCloudSource;
source.Datastore = fds;
lidarLabeler(source);
Hope this helps!
