This is the law.

Below is the law, and points out exactly why the officer
was in the wrong.
I am unable to locate any section that states bicycles
shall ride single file.

21202.  (a) Any person operating a bicycle upon a roadway
at a speed less than the normal speed of traffic moving
in the same direction at that time shall ride as
close as practicable to the right-hand
curb or edge of the roadway except under any
of the following situations:
(1) When overtaking and passing another bicycle or vehicle
proceeding in the same direction.
(2) When preparing for a left turn at an intersection or
into a private road or driveway.
(3) When reasonably necessary to avoid conditions (including,
but not limited to, fixed or moving objects, vehicles, bicycles,
pedestrians, animals, surface hazards, or
substandard width lanes)that make it unsafe to continue
along the right-hand curb or edge,subject to the provisions
of Section 21656.  For purposes of this
section, a "substandard width lane" is a lane that is too
narrow for a bicycle and a vehicle to travel safely side
by side within the lane.
(4) When approaching a place where a right turn is
authorized.
(b) Any person operating a bicycle upon a roadway
of a highway,which highway carries traffic in one direction
only and has two or more marked traffic lanes, may ride as
near the left-hand curb or edge of  that roadway as practicable.