First half is how a differential works. 2nd half comes to the conclusion that cost is the constraining factor.
$500-1000 on top of the cost of a three motor Cybertruck doesn't sound onerous to me. He doesn't mention that Jack Rikard [RIP] acquired the North American franchise for the Quaife torque sensing differential for the Tesla Model S. It's on the EVTV catalog:
EVTV Motor Verks Store: Quaife ATB Limited Slip Differential for Tesla Model S, OEM Electric Vehicle Items, QuaifeATB.
Their $1,795 list price tracks with his $500-1000 estimate.