Ive already been down that route and it wouldnt be an expungement. (at least in California) Those are typically saved for felonies. My attorney in Cali said it would be a dismissal at most. It was an infraction, think $100 speeding ticket. Same thing.
Was your CA attorney considering that you don't live in CA? Many laws in many states say "or a similar offense in another state." They don't really care about the other states' punishment but concentrate on the offense.
I was thinking more along the lines of potential employers who may use a national background check supplier rather than a state source, though.