This probably violates countless landlord-tenant and zoning laws already on the books in L.A. Of course, in this instance, it would be the gubmint violating said laws, wouldn't it?
I have years in multi-family real estate brokerage. Single family here typically means "1 on a lot," going to 2,3,4 on lots etc.
Usually there is a minimum lot size measured as sq. ft. per unit. These values are not the same from jurisdiction to jurisdiction. (There can also be other measures, like feet of frontage (the width on the street), set backs on four sides, etc. Also percent of lot covered by structures.
People very likely have misconceptions about the entire City of Los Angeles. It has some crap-hole areas, and some really nice ones too.
For something like 15-20 years there have been provisions for "granny flats," which allow a 2nd unit on a single family parcels, for another household. That means cooking. The most common means of permitting a 2nd unit is the cooking exhaust system.
In a single family house it was permissible to rent out a room, to say a college student. But when it came to his/her cooking, you could not add a separate range with exhaust.
Obviously frequently folks don't observe all these rules. In wealthy Newport Beach for example,, weekly rentals are very lucrative. Creating small rental spaces is done without zoning or permitting.
And at the other extreme, in poor areas sleeping/living quarters are often "bootlegged" in garages.
Heads up: If it is happening in California, it might be headed your way, too.
When they say "Los Angeles," it is the jurisdiction of the City of LA, some 4 million, the 2nd most populous city after New York City.
The County of Los Angeles is just over 10 million. 4,751 Sq. Miles. It is the most populous County in the US.