I'm not a complete believer on BTC, but I do have to acknowledge the fact that there is a non-trivial chance this is competing and might even replace gold one day (among millenials and Gen Z'ers, it already happened). If it does, its going to the stratosphere. Not much different from a startup that brings a new tech, changes the world and sees a gigantic multiplication of capital for its shareholders.
So while I agree with him that the reflexivity can lead to these boom bust cycles (exacerbating them), I find it dangerous to call is a ponzi, because that will lead one to to make investing and trading mistakes. He is going to sell it too soon, not rebuy it or short at some point and he could pay the price. I suspect deep down he is afraid of being an "idiot" who went long and lost money, so he calls it a ponzi to distance himself from other longs and make sure he takes his profit
I rather call it a potential revolutionary, but risky, tech. I limit my exposure but I want to be there for the whole ride if it does the tech does work