Well first this doesn’t really have anything to do with the article.

But to answer your question:

Be in a situation where your central bank (they can’t get bankrupt as they literally print money) doesn’t give interest (negative interest even better)

Be big, financially competent and trustworthy enough that no one doubts that you can pay back any loan.

Now people that have too much money and need a convenient place to store that money without too much costs buy your debt for more than what it’s worth.

Profit.