Forgetting that most is fake, a lot of it is made by traders who buy sell buy generating a volume that day 10 or 20 the actual size of their stash.
Why is most of it fake? That was true in the heyday of the Chinese exchanges who had no-fee trading -- they had millions of BTC traded in daily volume. There is no comparison today. The highest volume exchanges (Bitfinex, Okex, Binance, GDAX, Upbit, Bitflyer) all charge fees now.
Leveraged orders = liquidity that all of us can buy and sell into. So it's just as "real" as spot trading volumes.
Lately I've become a pessimist, that might be one of the reasons
Joking aside, I don't consider 0 fee volume fake as long as it is done by real people.
In the case of Huobi it was volume made by scripts , and I suspect that a lot of exchnges are amplifying their volumes by various means even now.
In case of Huobi (or OkChina, I don't remember that well), there were times when it was just multiplying the orders or adding trades that did not reflect on the walls.
Why I still believe this is that we had quite a few pretty weird situations where the volume didn't spike an inch but the price moved 10 times more.
It's insane and from my point of view pretty unnatural to have 1000 BTC moving around at 10500-600 let's say an then just 100 BTC to drive the price down by 500$, and I'm not referring to a sudden dump.
But in the end... what is natural in the BTC world