actually from the official BTRFS wiki, it's written that the toplevel subvolid is 5. The quote :
The top-level subvolume (ID5) (which one can think of as the root of the filesystem) can be mounted, and the full filesystem structure will be seen at the mount point; alternatively any other subvolume can be mounted (with the mount options subvol or subvolid, for example subvol=subvol_a) and only anything below that subvolume (in the above example the subvolume subvol_b, it's contents, and file file_4) will be visible at the mount point
So you should either mount the filesystem without any subvol or subvolid option like this :
sudo mount /dev/sdc3 /mnt/temp
or explicitly specify the subvol of the top-level, which is 5 (not 0).
sudo mount -o subvolid=5 /dev/sdc3 /mnt/temp
In both cases you will end up with the top-level subvolume mounted.