Solid bed,dot and dabbed leaves to many voids which in turn gives you cracked and broken tiles,he might have been doing it for twenty years but he's being doing it incorrect for twenty years.
It's amazing his tiles havn't fallen off.
Not only does d'n'dabbing leave holes, not combing the adhesive means it has no mechanical key to bond the adhesive to the substrate.
He's been lucky, and a bit slack!
Dot and dab is not an acceptable method anywhere. Just think of the voids, weak areas and what can breed in those areas.
Just because he has done it this way for years doesn't make it right.
All tiles should be fully buttered if there is an area where the trowel does not fit the wall still needs to be covered in adhesive I have a few narrow trowels for this purpose I have even made some up out of paint scrapers there is no exscuse for dot & dab it is very bad practice.