It's true, there is a difference with California legal and Federal legal emission requirements. And, for the most part California is stricter. However, a USED vehicle (such as this 2005 VW Passat) which has all the Federal required emission components, can pass the California smog inspection process and be legally registered in this state.
It is true that California cars have different, and in some cases more, emission components then Federal cars, but this does not mean that these cars can't be registered in California. So long as the vehicle runs well, has no emission system tampers, and it passes the smog test (emissions results are below California's Emissions Cutscores) it can be registered in California. The Emission Cut Scores are not much different then of those in other states. As mentioned, if the car is running right it should pass the smog check.