I interpreted it as, there are skills (in the water and out) that you should have in order to dive solo. You should have those skills down cold before you ever start diving solo. Your dive planning, your management of redundant gas sources, how you choose to provide redundant buoyancy and how you deploy and use it when needed, etc.. All those things are things you should be totally facile with from practice in a buddy diving context before you start diving solo. Anything he has to teach you would mean that you have just learned a new "skill" and you should not be certified to go out and dive solo where you would be relying on any skill that you just learned.
He could teach a student how to carry a pony bottle and use it. His position seems (to me) to be that, while he could teach someone that, he would not certify someone to dive solo who has no more experience in carrying and using a pony than just what they got in a solo class. He wants them to have more (and real-world) experience with it than that. And, I guess, he doesn't want his solo class to last a month and have a whole bunch of OW dives just to get his student the experience he thinks they should have.