He uses fiat credit cards. I assume he then converts Bitcoin to USD every month to pay the balance. I currently keep a couple months of fiat for fiat bills around, but he is skipping that step by just using their dollars instead. I also assume he earns in Bitcoin given his company. That's a lot simpler than getting paid in fiat, converting to Bitcoin, and converting back to fiat to pay a credit card.

Frankly, if you plan to pay taxes, using his method is a lot simpler. You have one taxable event instead of many like with the cards that convert to USD every time you get a charge.