I believe you are re to cpc sec 171b. No guns in public buildings.
from cpc, sec 171b
(c) As used in this section, "state or local public building"
means a building that meets all of the following criteria:
(1) It is a building or part of a building owned or leased by the
state or local government, if state or local public employees are
regularly present for the purposes of performing their official
duties. A state or local public building includes, but is not limited
to, a building that contains a courtroom.
(2) It is not a building or facility, or a part thereof, that is
referred to in Section 171c, 171d, 626.9, 626.95, or 626.10 of this
code, or in Section 18544 of the Elections Code.
(3) It is a building not regularly used, and not intended to be
used, by state or local employees as a place of residence.
You will see that a restroom does not meet that law. As we do not have state/gov't employees that regularly present in restrooms that I know of anyhow.
I would also hope that no state employee uses a r/r as his own place of residence.(joke)
Hope this clears it up a little for some.