Every merchant in the US is required advertise accurately. If they're selling a car in CA and stating that it has 300 hp, then it goes without saying that it has to run on the available fuel in CA. Unless there's a blurb and an asterick in their specs that state CA cars are making less than 300 hp, then it's misrepresenation.
Look in the owners manual, it says 93 is required. There is no misrepresentation if 91 doesn't produce 300hp. ...my$0.02 anyway.