I was writting a long answer but finally, I decided to simply quote:
> In the court's view, royalties are those items which constitute passive income, such as the compensation paid by a licensee to a licensor for the use of a Page 7 patented invention.
https://www.irs.gov/pub/irs-tege/eotopicd89.pdf
Also, as you say, some royaltie are active incomes. But Passive royalties exist.