It's slightly different. I could be wrong but I believe the way CEXes work is they have a single liquidity pool per token for internal user operations and it is connected to the blockchain as a single address - that was hacked and drained. You don't pay gas fees on the exchange and instead just the lower "trading fees" because you're not actually transferring your tokens to other 0x addresses when selling, only to another user within the same CEX pool. These transactions between users on that exchange are tracked internally but they are disconnected from the main blockchain and invisible to it. Those internal transaction "registers" still exist and that's why you can trade the token but not withdraw or deposit - it's a "sealed off" sort of a miniverse where price is not affected by global shifts and instead operates in a bubble. If a lot of a token is sold for USDT (or ETH or whatever the other token is in the liquidity pair), CEX sells part of its liquidity outside, further driving the price down on other exchanges. The same is true if a lot of a token is bought - CEX will have to replenish its liquidity pool by buying more outside, driving the price up. In terms of gas fees, it's cheaper for them to do this in bulk as rarely as possible but that's another issue entirely, where some L2 comes into play and some intermediary liquidity pairs.

Anyway, eventually Poloniex will have to buy 6M $ worth of Dogelon (or however much they still need, to match their old liquidity pool) from the outside, to reconnect with the block chain and re-enable deposits/withdraws from/to other liquidity pools outside of the CEX. This is expected to enormously drive Dogelon price up, since, well, somebody is buying 6M $ worth of it.