I did notice a couple of things in the linked report, first, as usual the report makes no distinction between assault rifles and assault weapons.
Second was that part that implies that while the State does recognize that assault weapons have sporting use, that use is overwhelmed by their potential for harm, and that's why they are banned.
Guy buys the rifles in AZ (apparently legally). Fine. When he brings them into CA, he has just broken CA law. Compounding things is the fact that apparently he did not register them in CA, either. Not sure how this applies, but the report specifically said they were unregistered. It might be that the particular rifles might have been legal to possess, had they been registered with the state (I rather doubt it, but I don't know).
He has a party with gang members in attendance. Shots get fired, in the air, and into a couple people. Police come, find illegal guns.
I don't see where this has anything to do with commerce. OR a CA citizen's right to keep and bear some arms.
All else being equal (and it almost never is) bigger bullets tend to work better.