Apparently this isn’t true with the containerd snapshotter anymore. the folder io.containerd.snapshotter.v1.overlayfs does not only have the extracted image layer folders, but also has the final mutable folder used as container filesystem. I guess the rootfs folder only mounts the containerd represenation of the conainer filesystem.
Please do not delete any folders you deem irrelevant, this might break the chain of extracted image layers required for a container file system.
You can try if ctr --namespace moby <ctr arguments> helps to detect it.
Worst case, you should be able to use a tool like bbolt (requires extra installation) to query data from the bolt database file metadata.db.