I have seen nothing of the sort on the Medical Board of California's website. In fact, while the Board does state that "[f]ailure to disclose a conviction is considered to be dishonest, and therefore an egregious breach of ethics and unprofessional conduct," it does not at any point explicitly or implicitly state that it is exclusively addressed with license disqualification and/or revocation.
California's Penal Code also provides little evidence of this claim, although it does address the necessity of reporting such a an expunged conviction when seeking licensure. California Penal Code, § 1203.4.(a):
...The order shall state, and the probationer shall be informed, that the order does not relieve him or her of the obligation to disclose the conviction in response to any direct question contained in any questionnaire or application for public office, for licensure by any state or local agency, or for contracting with the California State Lottery.
No explicit or implicit statement of automatic license denial/revocation for nondisclosure of a felony conviction expungement.