edit: turns out they're not a non-profit.
Either way: 501(c)(3) status exempts a nonprofit from Federal income tax, but not necessarily state taxes. I don't know enough about California taxes to say whether or not that matters for them, but it's plausible that they'd have tax obligations from accepting securities.
Edit: Based on this search[1][2], there's a Benefit Corporation, not a 501(c)(3).
[1]: https://rct.doj.ca.gov/Verification/Web/Details.aspx?result=...
[2]: https://rct.doj.ca.gov/Verification/Web/Details.aspx?result=...
Looks like I was wrong.