I have not looked at the video.
I am assuming that the pallet wood is put on a table saw or other equipment to make a 1/2 inch board into 1/4 inch?
It is my opinion that nothing else is needed to preserve the wood similar to a wood fence.
Though as Timothy suggest that folks could use linseed oil.
Also charring the wood would be another way to preserve the wood.
I know there are several threads on this subject:
https://permies.com/t/242629/shou-sugi-ban-charring-technique