it's not just CARB its the standard set forth by EPA for nonroad-compression-ignition-2011-present vehicles it has to pass. But being he is in the UK if he doesn't bring these overseas to the US then he wouldn't have to bother with the US standards. I'm sure Euro standards are just as stringent though but i'm not familiar with their EPA environmental regulations so i can't say for sure. I'd have to do more research. Millbrook is just an orginization based in UK.
But like you said triumphrider, it has to pass this 100% he claims which i doubt it will unless they fudge the numbers or have a 'preset predetermined standard' that allows a range CLOSE to 0 or at least lower than previously used. There's always a loophole that allows such bold claims. So although it wouldn't be a 'true' zero emission, if it falls within the guidelines he can legally make the claim.
The legal mumbo jumbo set forth in the standard would allow people to make such claims unfortunately.
Knowing these basic things, people can be the judge on if they want to believe the actual zero emission claim or not. Those with even an ounce of common knowledge in IC knows it's all BS.