Germans don’t keep their cars very long; they trade them long before serious wear occurs. Many leave the country for Africa and other developing regions.
Europeans are obsessed with reducing wast motor oil; all oil in Germany has to be recycled!
You, as an owner, are mostly concerned with having the engine live a long and happy life. That is best done by changing oil at about 5000 miles for normal mixed driving. I would only go 10,000 miles if all my driving was highway.
So the mechanic is basically correct; he does not have to toe the environmenntal and sales hype.
However, if you want to pass the car off on someone else after 3-4 years, the 10,000 mile interval won’t hurt you, just the next guy.