Okay that makes sense about the cold and hot wallet. But if they are giving B2X after fork, how is not that giving free money? From my understanding, if you have 5 BTC, they will give you 5 B2X totaling: 5 BTC and 5 B2X.
That's true, but there's no value yet in the B2X, it's just an entry in an account. It only gains value when someone (outside the exchange) puts in an order to buy at a given price. When they buy, the B2X has a value - the money has not come from Coinbase, it has come from the buyer.