That happened to my niece & military husband...when posted in CA.
Living on-base, but they had purchased a car there....and CA is scraping everywhere for potential people who might have sought to evade CA taxation...even when not proper for their situation.
Forgot what they had to do, but, as noted above, calling FTB would be the first step to see if they want proof in some way.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
