Yes, correct; that's how Bisq works. I was wondering whether the platforms you've used in the past also worked like this or how they were technologically decentralized.
Etherdelta was probably one of the first exchange I used. It's basically a smart contract, hence the decentralization aspect.
The website is just a way to interact with the smart contract. Even if the website is down or completely cease to exist it would still be possible to interact with the smart contract via other tools such as etherscan or mew.