"shakyjay"......"nguyenbio" is correct. The mistake that is often made on this forum and others, is that people read/post excerpts from state laws, but don't realize most of those laws use "Case Law" to interpret things that are being argued here. In the State of California, a monthly publication is available to law enforcement that interprets laws and how they change when new cases arise. It's kind of like using the internet. You can look up what determines an open container in various types of vehicles. It will give you the latest interpretation by a State court.
This is simply a common sense issue. If you're driving and someone is in close proximity to you, like someone on a sofa, directly behind you and is drinking, you could theoretically be charged with open container. The woman who says she is sipping wine while her husband is driving. I would cite her.
Again, common sense.....the law is designed to prohibit someone from actively drinking in a vehicle while another person is driving. The concern is you're drinking/sharing that beverage.