So your'e saying that if i keep my coins back'd up in a wallet i cant get hack'd ?
Having a back-up do only give the access in your wallet when you do need. Like private keys or wallet.dat file. You can import it anytime if you do have these things on a certain wallet and you can access it once again this is why we should not easily give these keys or letting show on public. On the link above its just a basic stealing or hacking of your coins on an exchange wallet. This is why when we are using web wallets we should always set 2fa and dont store huge amounts on those kind of wallets.
That is pretty sure the right thing to do when you are using a web wallet because it is link in the internet and hackers can surely manipulate it, bitcoin is surely secure but with the skills and level of knowledge this kind of people have they can surely manipulate anything in the world wide web and the only secure option you can do is with the private wallet with your own private key.