The 230 mpg number is based on driving 50 miles. Of course, the first 40 are with the battery (infinite mpg), the last 10 are gas-powered (46 mpg).
12 gallon tank * 46 mpg + 40 battery miles = 49 mpg.
Leave it to the current administration to cook up a new way to compute mileage by varying the trip length. By that measure my old pickup truck gets over 30 mpg. It's a 1/2 mile downhill to my buddy's place so I can just hold the clutch in and coast down there with the engine off. When its time to go home I start it up and drive home.
1/2 mile at infinite mpg, 1/2 mile at 16 mpg. Overall, 32 mpg.