What does decoupled mean?

Normally through arbitrage bots prices tend to be harmonized between exchanges. If a decoupling event takes place it means arbitrage bots for whatever reason can not do their work and the price decouples. If the problem is not severe or can be fixed in a timely manner, the bots can start their work again and equalize prices between all exchanges - resulting in "the market price".

Now, what we see on HTX and Poloniex since their claimed "hacks" is that a decoupling took place, but prices haven't returned back to normal for days or weeks.

A concrete show case: https://coinmarketcap.com/currencies/monero/ ("sort by volume"). Or see it here: https://i.imgur.com/XWe1SJ1.png

Despite claiming to have the largest daily XMRUSDT trading volume of all CEX the price is ~$2 cheaper on HTX than on all other exchanges with the exception of Poloniex.

Together with Poloniex they claim to have 33% of daily (wash trading) volume of Monero. But then you look at the order books and you see it stacked with ridiculous low amounts of (paper) coins on a day that not even sees a +2%/-2% movement.

Now we have plenty of data to compare (healthy) exchanges with troubled ones. We know that volume, price and number of real coins held by an exchange are connected and can be represented through each other. If something is off it is easily recognizable like in this case. Something doesn't add up. Prices should follow liquidity. But if like supposed their is no real liquidty but wash trading with paper coins to attract new deposits it's a severe red flag you should know about.

Do not trust. Verify!