I make grilled octopus frequently and I’m not following his steps, either, or their purpose. I’ll also throw out there that grilled octopus is one dish that does not benefit from sous vide. You can easily prepare the octopus for grilling in a fraction of the time by throwing it in a pot of simmering/slow boiling water for 30-50 minutes to tenderize it. The time will depend on the octopus and how tender you want it, and not using sous vide gives you the flexibility of checking it as it goes (with a knife poke) to confirm when it is done.
My recipe: Place enough water in pot to easily cover octopus. Salt until it tastes like light sea water. Throw in half an onion, a few cloves of garlic, a couple of bay leaves and a tablespoon or so of black peppercorns. Bring to a boil, throw in octopus, cook for 30-45 minutes until tender. Remove and let cool enough to handle. Depending on the octopus there may be extra skin which is somewhat gelatinous - remove if desired. Toss in some olive oil and herb (fresh or dried oregano, marjoram or thyme), grill, serve with a little lemon or red wine vinegar and more EVOO.
Bonus: When you cook in a pot you end up with a bunch of delicious octopus stock which can be used for soups, chowders, or a seafood risotto.