Use stat to display the file system status, following links, and output the format as the human readable file system type:

#stat -f -L -c %T /tmp
ext2/ext3
#
# stat -f -L -c %T /mnt/fileserver/volume
nfs
#

As suspected “/tmp” is a regular ext file system, but the path “/mnt/fileserver/volume” is an nfs mount. What happens if we unmount the nfs mount:

# umount /mnt/fileserver/volume
#
# stat -f -L -c %T /mnt/fileserver/volume
ext2/ext3
#

It reports properly that the directory is just an unmounted directory in a regular ext file system.

Alternatively you can use the mountpoint command:

# mountpoint /tmp
/tmp is not a mountpoint
#
# mountpoint /mnt/adfs40/vol1
/mnt/adfs40/vol1 is a mountpoint
#
# umount /mnt/fileserver/volume
# mountpoint /mnt/adfs40/vol1
/mnt/adfs40/vol1 is not a mountpoint
#