Earlier quoted context omitted.
The nominal market cap of BTC right now is about $129 billion. A $40m trade represents about 0.03% of the reported market cap. That a trade that small would cause the market to crash by double digit percentage points is absolutely a sign of a thin market. Also, the slow speed of price propagation isn’t a sign that the market is thick, it’s a sign that the market is inefficient.
That's not a relevant percentage. You'd need to look at the amount of Bitcoin that trades regularly. Also, I wasn't saying anything about slow speeds. I was saying that the ability of the market, on a single smaller exchange, to absorb a $40 million trade in 20 minutes is not traditionally what you'd call a thin market.
To the point that, hmm, you could just trade with yourself to pump or dump the price.
A market composed of yourself and yourself is, by any measure, pretty thin.