I hadn't heard that re: 3 wheel vehicle licensing angle, but that sounds plausible as well.
Look for the state legislature to remedy that sometime soon in the future. ;-)
There are 3 classes of motor vehicle operator licenses: A, B & C. Any class may operate a motorcycle with an M1 endorsement. Operation of a motorcycle plus sidecar requires a Class C license which Schwarzenegger apparently posses or once possessed. He lacked the M1 endorsement available by either practical, driving test or completion of a safety class.