The summary is not a rule book.
Your question seems to assume that every cat must be following the summary to a tee.
Tongue in cheek, I want to point out that cats can't read.
And even if they could, not every pet owner will share this link with them.
And even if they do, there are no repercussions for refusing to follow the guidelines anyway, so there's no way to make them follow the rules.
Cats usually follow their instincts.
They then dig for a short time, turn and squat near the area of digging, turn (perhaps also smelling their waste) and dig once again.
Why do cats do that? Simply put, they try to hide their presence in their environment. Part of that entails making sure that you can't smell their droppings.
Contrast this to dogs, who have no habit of sneaking around. They bury their food and belongings (to keep it safe from others) but they have no reflex to bury their droppings (because they're not trying to hide).
It's an instinct that cats have received from their ancestors. Most cats retain this instinct even if they live in an environment where the behavior is not necessary.
However, as the drawback to failing to do so is no longer applicable (at least for house cats), there is less incentive to keep this instinct. Over time, cats may lose the instinct, the same way that human ancestors lost their tails over many generations.
We have 3 cats, all of whom are rescues that were initially raised in the wild. To my surprise, all three of them have excellent litter box manners without us needing to teach them. It seems like living in the wild has reinforced their "must hide smells" instinct.
If we've forgotten to clear the litter box, they stop using it at some point. However, they still hold it for as long as they can and don't just do their business elsewhere. I've seen them sprint to a clean litter box after holding it, and they've on occasion even fetched us to clean the litter box for them (similar to how they lead you to an empty food bowl).
Some cats don't.
Either because they lack the instinct, they go against it, or there's a more pressing reason for them to do things differently.
Two of our cats are sisters, M and C. C is clever and very pedantic about pretty much everything, including burying droppings. M clearly does not understand the purpose of burying droppings.
Initially, M did not bury anything, and C would actually go in after M to bury it for her. After a while, C started reaching in the litter box while M was still doing her business, clearly trying to teach M how to do it herself. You could see her try to set the right example.
M understood that C wanted her to do something, but she still doesn't understand what the goal is. So she has actually ended up learning the wrong lesson. When she uses the box now, M swipes her paw at everything inside the box: the walls, ceiling, even the door (which flails around as she does it).
She clearly doesn't understand the necessity of hiding her business; but she does acknowledge that her sister wants her to perform a swiping movement with her paw. But, as I see it, she thinks it's a matter of cleaning the box, not hiding the droppings.
Tangentially, even humans can't agree on toilet habits.
Even humans have differing toilet habits. Read these responses on Reddit, when they were asked whether they sit or stand when they wipe after using the toilet.
Notice how everyone swears by their own method, and thinks that the other side of the discussion is clearly doing it wrong.
Humans have the benefits of spoken conversation and a strong reliance on teaching each other, yet we still all do it our own way. It will be no different for cats, they simply do what works for them.