He had assistants that would "prepare" his students with the proper technique before they could even have lessons with Auer.
This really seems true. If you are struggling with a technical passage in a piece and you don't really master the difficulties, it shows. You can tell when a violininst has conquered his technique and can just play and let the music flow.
This book is a fantastic read. We can all learn a lot from the greats. They are not all in here, but enough information is shared that would benefit any violinist.