If you're not paying for it you are the product.
Signals money comes from two sources:
1. User donations - you can in fact be paying for it,
2. A 50 million dollar initial fund provided by a benevolent sponsor, and probably some other misc funding
It does not come from selling ads or user data, which is the usual meaning of that glib saying.
That doesn’t relieve one entirely of fears of betrayal. American 501c3 law allows nonprofits to act like ordinary for-profit corporations in many ways. Such organizations cannot generate a profit (which has a specific legal meaning) but they can amass money to pay as much as they want in salaries to their leadership under employment contracts, or use that money for things that none of the original supporters saw as part of the mission. The community’s insight into finances is limited to peeking into periodic tax filings instead of having insights into (and any oversight over) day-to-day operation.