Yes and no. You can also earn bitcoin on other ways, there are for example companies that offer blockchain services. They make money by offering services so they don't trade.
But in essence the only way to make money is by buying and/or selling. Every company sells something direct or indirect. Can be products or services. There is not really another way to make money.
That is i think one of the reasons why smart people are not necessarily rich. It's better to be a good merchant than a rocket scientist. Einstein was not that rich, Jeff Bezos is. How does that come you think? Because he's the best at what everyone else is also doing, selling things online.