What if the statute contains a 10,000 page table listing the tax payable on every possible purchase price, to the nearest penny? Written out in "longhand" format [e.g. "If the vehicle price is between twenty thousand five hundred eighty-three dollars and thirty-five cents, and twenty thousand five hundred eighty-three dollars and forty-four cents, the tax payable shall be two thousand, fifty-eight dollars and thirty-four cents. If the vehicle price is between twenty thousand five hundred eighty-three dollars and forty-five cents, and twenty thousand five hundred eighty-three dollars and fifty-four cents, the tax payable shall be two thousand, fifty-eight dollars and thirty-five cents.] for all values of vehicle from $0.06 to $250,000. Such language would be a genuine part of the statute, though I'd hate to be responsible for reading through it to ensure there weren't any "surprise" taxes or tax breaks for certain prices of vehicles. How could one argue that such language wasn't legitimately part of the bill? Is there anything in the laws or constitution of the state of California that require legislators to be concise?
No, you are confusing a referendum with an initiative. An initiative is a voter-sponsored measure, and it indeed must deal with a single issue. A referendum measure is a vote by the people on a bill passed by the State Legislation and signed by the Governor (or passed over his veto); it deals with whatever happened to be in that bill, regardless of whether it involves more than one issue.