It’s incredibly hyperbolic for effect and not meant to be taken as a literal statement that you never see it. MM/DD is the most common and you will confuse people writing DD/MM. It’s also so common to use two digits for year that they had to warn people to put all 4 in 2020 but it has become more common now to see 4 digits after everyone got used to itI was starting to feel like a crazy person. I have only ever seen YYYY-MM-DD used in my field of work.
This is incredibly inaccurate lol.
Edit:
And to weigh in on the logic behind which one is best, YYYY-MM-DD is the ISO standard because it is the only one that allows files to self-sort chronologically.
ISO standard definitely is used where that format is required and makes sense for document self sorting. I see a lot of manually dated documents and rarely see anything other than MM/DD/YY or MMM DD/YY (where the first one is the abbreviation instead of a number)