Hi John, that sounds like method known as a shallow bury, using a ruggedized Fibre cable. 200mm is the correct depth for this and the cable will look like this (sorry old pic)
It's one of the standard install methods Chorus use to install Fibre.
I am really supprised that that is allowed so shallow when a spade could go through it with ease, also tacked along a retaining wall where a weed eater / wipper snipper could regularly come in contact with it.
At that depth I would have thought mechanical protection would have to be put on top of it, say 10mm H4 treated wood.