I'd rather believe that some exchanges fake volumes (and they do) instead. I think your fear is way more possible with companies like PayPal selling coins they never let you withdraw.

Here's how exchange orders look:
-> BTC/USD pair is listed on Exchangeus. You are the first to sign up there and deposit your 1 BTC. You place a sell order: 1 BTC for $2k. Alice comes up and wants to purchase BTC but your order is the only one that exists on Exchangeus. Alice deposits $2k through her bank account and places a buy order, filling up your sell order entirely.
-> Bob comes up and decides he doesn't want to sell at $2k because he thinks 1 BTC at $2k is cheap. Bob has 10 BTC in his personal wallet. He deposits his 10 BTC on Exchangeus and places an order for $100k per coin. There goes a sell order worth $1M.

But just because Bob wants to sell at $100k per coin does not mean BTC will ever touch it. Perhaps by the time Bob remembers he placed a sell order, Bitcoin will in fact drop to the floor and be worth $0.01 per coin. Bob's sell order still remains alive though. Although Bitcoin's fully dilluted market cap is now worth $210k, Bob's order is still worth $1M. He's still waiting for it to be fulfilled, yet that does not mean it will ever happen.

Now let's say you and Alice go over Exchangeus again. You are the only Bitcoin traders there. Suddenly, you start continuously buying & reselling 1 BTC a hundred thousand times. The volume you create is worth 100k BTC, but the reality is.. just a single coin has been moved. Although the volume is that high, it does not mean this many coins have been moved around.