The video was made by the Jam Handy organization. They did videos for several car companies, and sometimes a consortium of them, is my understanding https://en.m.wikipedia.org/wiki/Jam_Handy
That would explain the abundance of available mini-models that they could machine.
That does take the wind out of the sails of the argument that it could've had a broader focus than just the differential engine. In that case I'll shift my dismay to "90 years ago, videos of this caliber were possible, and yet educating people on a broader scale didn't enter the minds of any entity which could've afforded it."
The video was made by the Jam Handy organization. They did videos for several car companies, and sometimes a consortium of them, is my understanding https://en.m.wikipedia.org/wiki/Jam_Handy