The way they built the wall is ok as shown in your video link, it should be fine for many years and Villaboard is suitable (over lap the sheet 50 mm to stop earth leakage to fence. But a raised garden bed next to a timber fence can be a termite 5 star motel and eat the fence. Have you ever seen big ants with 20mm wings in your area? They are termites on scout.
Wall upgrades if you wish
I personally would make the footings cement with trench mesh for a forever wall Footings 100mm - 200mm deep, by 300 wide. They are using gravel sand and cement already for footing why not mix it all together and make a footing if you have that skillset.
I found on several occasions liquid nails is effected by water and stops bonding I might use regular tile glue instead or thin mortar
I personally also buy and install Besser bricks 390Lx 190H x 90W a thin half brick as they are cheap to make a back wall to the garden instead of versa board so its all solid and free standing install the same way as front bricks I use pavers as capping if required. This means a footing all the way around.
One day all fences will need to be replaced if the villaboard is attached to the fence it will be ripped out with the fence or damaged your garden earth will partly collapse and it will cost you much more to put in a new fence if the fencer agrees to a larger quote to restore you raised garden bed. Consider your neighbour will be paying half that cost too.
Solution use cut up strong in expensive color bond fence posts(Spray paint cut edges) along the inside of the villaboard (Villa board touching the fence as per video support two ends and two posts in the middle dig post in 300mm back fill the earth will compact to color bond post ) and attach the villaboard to the color bond posts. So the whole ideas is the villaboard is free standing if the fence is removed in the future.
Well some food for thought the original how to on that video will give you a new raised garden bed. And Villaboard will work to answer your question better is a bricked in garden all the way around.
It's great that you've received excellent advice from @Jewelleryrescue. All the points they mentioned are spot on, it's important to think about this garden bed in the long term. You also want to make sure that the materials used will not rot or degrade. My only suggestion for this build is to use the same material used at the front. It would also be prudent to leave a gap at the back of the garden bed so that rainwater does not get trapped behind it.
Here is a link for ideas and inspiration: Top 10 most popular raised garden beds
If you have any other questions we can help with, please let us know.
Those blocks cost a bomb $10 to $15 each thats why suggest besser half width at $3 each plus half width gives you more garden space in a tight spot. You will never see the gray bessers once plants grow.
But besser bricks best to use mortar and those others dont so there is pros and cons. Some of those garden shows cut too many corners for the longer term results.