One serious error that man makes is "off-list" lowers... California comprehensively banned ANY AR-15 pattern rifle with the "evil" features. What makes that legal is the stock type.
Yes that is accurate,
but, California also banned some lower recievers by name which means that even if he had set the rifle up in that same configuration, but used a listed lower reciever as per the ban, the rifle would be considered an "Assault Weapon"

and would be illegal (for the most) part to own. Thanks to the Harrot v. Kings County decision, California cannot ban lower recievers by type (e.g. AR-15, AK-47) they can only ban by combination of feautures and by specific makes and models on a publicized, state-maintained list.
This link explains it mo' better...
http://www.calguns.net/a_california_arak.htm (mo' better, another sign you've been on AW too long!)
Here is the Kasler List that defines which make and model lower recievers are banned
http://ag.ca.gov/firearms/infobuls/kaslist.pdf
Category III assault weapons are defined by characteristic features listed in PC 12276.1:
RIFLES:
A semiautomatic centerfire rifle capable of accepting detachable magazines and any of:
▪ a pistol grip protruding conspicuously below the weapon’s action
▪ a thumbhole stock or folding or telescopic stock;
▪ a flash suppressor, grenade launcher or flare launcher;
▪ a forward pistol grip.
A semiautomatic centerfire rifle with overall length of less than 30 inches;
A semiautomatic centerfire rifle with a fixed magazine holding over 10 rounds.
Here is another good reference list
http://www.tenpercentfirearms.com/index.php?main_page=page_8