but he is not sending bitcoin! he is sending the private key. it is like giving someone key to your home and to the safe in the wall so that they can go there and take the money you left them there. well that is not sending bitcoin.
additionally he is using shortwave radio so i wouldn't call that exactly "offline", that is just another digital form of transferring data. not to mention this whole thing is super risky since it can be intercepted in the middle.
So in short if thats me im going to create a new wallet then send the amount you want to that address and give to someone that address (this is how I get it).
Even you can do that transaction offline the receiver will still need to go online to get the money, I cant think of any possible way to make a bitcoin transaction offline it is impossible because if it can be done offline it will be easily hacked by other people and take the amount they want.