An offline computer, running ubuntu, would be one way to securely generate a wallet:
Ensure the wallet is created with a pass phrase, dump the keys (and be sure you have the private keys all written down/printed correctly) then wipe the computer HDD.
(don't use an SSD, since most people don't understand how to properly wipe an SSD)
It's simpler to just remove your hard drive and use a live OS, especially Tails, since Tails will automatically delete all session data. And I would never print a private key, who knows what sorts of backdoors and security vulnerabilities a printer might have?
People mostly think that just because a paper wallet is offline that they're already safe, even though a lot of people mess up the process by leaking the private keys while generating the wallet.
I'm amazed that after so many years, people still that paper wallet in the form of printed-out private key is the best way to store their coins.
Don't promote this scam website.