At the time it suspended it, the company was quoting a price of about $8,500.
Trade of Bitcoin Cash was frozen just four minutes after it began on the firm's Global Digital Asset Exchange (Gdax) and existing orders were cancelled.
So the prices more than doubled in just 4 minutes. It might not even be a case of insider trading rather very, very thin order book.
That is why this happened:
> Update - All BCH markets will remain cleared and offline until 9am PST 12/20/17. At that time, BCH markets will enter post-only mode for a minimum of one hour to allow liquidity to be established.
That is to say no matching orders allowed of any kind - limit or market which can suck the liquidity and cause a huge price jump.
One might think that Coinbase/GDAX understand liquidity and market making after so many years. But no. Makes you wonder what kind of stuff is going on in other exchanges.