It’s about taking steps to earn trust. Open Sourcing the code is one step, yes. Because you’re allowing people to run their own code if they want to. But like U said above there are other ways of earning trust if you don’t want to open source code.
It’s not “all or nothing” with trust. If you hide your identity, have a scammy website, AND don’t share the code… well that’s three strikes in terms of earning trust