If you only have a cloud wallet account and follow this guide to create a "backup" you're not actually backing up anything, you'll simply create a backup of an empty wallet containing no private keys.
Also, there's no point in actually doing this since the security of your account is not improved, in fact you only open another vector of attack which is through your bin file and the presumably weaker password you've set for your wallet.
But to correct this guide: in order to backup your cloud wallet account using a bin file you would have to do the following:
- Login with your cloud wallet account and go into your permissions page and write down your active, owner and memo private keys
- Go into the settings, then switch to local wallet mode
- Create a new wallet (unless you already have one)
- Settings > Restore > Import Private key with each of your private keys from step 1
- Now you can create a backup bin file
Even after doing this, the brain key of this wallet is useless as it doesn't correspond the private keys of your account.
RE: User Guide -- How to create a Backup file (.bin) first time.