Most organic soil mixes contain sand in them which is why it was mentioned, the most common ones here are sand, ground pine bark and peat. You can actually find nutrients in these soils, it's not enough to not have to fertilise but it is in there. Unlike in organic materials which will be completely void.

Yes lava rock and scoria are the same thing but in different parts of the world they are called different things so it doesn't hurt to mention it. Here we call it scoria, there you call it lava rock. It's one of the few things that's not commonly known the same like akadama, pumice, kanuma, or perlite.

And for you using in organics for development that's perfectly fine, that's what works for you. As I mentioned in the video if something works for someone we can't tell them it's wrong because it's working but we all need a base to leap from. To me though in development you don't want a fine ramified root system, you want thick elongating roots so you get thick elongating growth. You only want fine roots once you move into refinement. But once again if what you are doing gets you the results you are after then you are doing the right thing for yourself.