The "compensation element" of your exercise might be taxable by CA. The various actions available to you when you exercise NQ stock options can be complex. See the excellent TurboTax FAQ on the subject at:
https://turbotax.intuit.com/tax-tools/tax-tips/Investments-and-Taxes/Non-Qualified-Stock-Options/INF...
If not taxable, then you would have to file a non-resident CA tax return to recover the CA income tax withholding.
