The [tenants guide][1] distributed by the California courts
addresses this (partially) on p. 21

> The rental agreement may be oral or written, however, it is strongly
> recommended that the parties have a written rental agreement. The
> landlord is required to provide the tenant with a signed copy of the
> rental agreement within 15 days of its execution. The landlord and
> tenant should retain copies of the signed rental agreement for their
> records. An oral agreement is an agreement where the terms are agreed
> upon by spoken communication. This is in contrast to a written
> agreement where the terms are set forth in a written document. A
> tenancy term of more than one year must be in writing. Oral agreements
> for a tenancy term of more than a year are unenforceable.

Text messages are a form of writing. However, looking at the bits of code in the associated footnote, [Cal. Civ. 1624][2]

> (a) The following contracts are invalid, unless they, or some note or
> memorandum thereof, are in writing and subscribed by the party to be
> charged or by the party’s agent: ... (3) An agreement for the leasing
> for a longer period than one year, or for the sale of real property,
> or of an interest therein; such an agreement, if made by an agent of
> the party sought to be charged, is invalid, unless the authority of
> the agent is in writing, subscribed by the party sought to be charged.

("subscribed" means signed). An unsigned written 2 year lease is invalid, so by default the only lease that exists is a month-to-month lease. That is sort of what the attorney was saying.

  [1]: https://www.courts.ca.gov/documents/California-Tenants-Guide.pdf
  [2]: https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=CIV&sectionNum=1624.