If piano technique is just technique....?

good music making is first a craft and then an art. You can't have art without the craft. There are hundreds of methods devised to help people learn the craft of their particular instuments, some of them are really effective, and others just diddle around. Learning by ear, as you described is a very slow and not so efficient way of doing things. If the kid in the story is very young ( like 3 years old) it would work, but watch out- 3 year-olds pick up things awfully quickly and demand more. There are plenty of books at the music store for beginning piano, and if the teacher should happen to flip through it before he gets to work with the kid, he might pick up a few tips on how to go about teaching- which is also a craft. There are lots of professional musicians who make rotten teachers. They know what they are doing and how it feels and how they express themselves in music, but it's hard for them to communicate that to others in words. some people who are less talented as musicians make better teachers- they have had to work out the teaching details in their own heads first. ( the best of course is a pro who is a stunning teacher- really rare)