No, with cold minting you still need to be online. Otherwise the network can’t see your blocks and you can’t see other’s blocks, so you’d build your own chain that can’t compete with the network chain and all your blocks would be orphaned.
But with cold minting you can mint with a key that cannot spend your coins. Your spending key can be kept safely in cold storage. So you can’t lose your coins if your minting-only computer is compromised.
Indeed Jordan doesn’t want cold minting in Nu. But for my part I’m in favor of including it.