Yes, it's a Toyota. And, no, it isn't exactly. Controversy!
BMW developed the chassis on which its Z4 and the Toyota Supra roll and provides the engines. Toyota did its own styling and tuning, so it can be said without argument that the two are not the same car. They are both built by Magna-Steyr in Graz, Austria.
Unless converted, it is not electric. The owner is clearly a contrarian, because (my stereotypical view) owners would make such a car louder, not quieter. And even unmodified it should make some sound. Perhaps LA noise (traffic and other) was drowning it out?
We have the Best Guest Commentators in the world!!!! Thank You, thank you. I was VERY curious about the license plate...I really appreciate you solving this puzzle.
Also, now that you mention it, the sound of this vehicle accelerating from a standing stop to substantial speed was....nothing, nada. I did not think about it at the time but there are a number of super fast vehicles in my area...the maker of the cars, unknown. I am presuming that this is electric....but damned if I know.
I have tried to find this on various BMW sites...but this search has been unsuccessful.
I think it is something else, but I don't know what. But still thank you very much. Traveller