He avoids capital gains in the article by using a MakerDAO CDP. This is a loan that is collateralized by his Ethereum holdings. (IIRC 1.5 ETH to the amount of DAI you want)
If the value of the ETH collateral that you deposited drops to less than 150% the value of the DAI you withdrew, anyone can come in and "liquidate" the vault, forcibly selling the ETH to buy back the DAI and charging you a high penalty. Hence, it's a good idea to have a high collateralization ratio in case of sudden price movements; I had over $3 worth of ETH in my CDP for every $1 that I withdrew.