2 key sentences in the article say so much: "Several said Model X, Model S and former SolarCity operations seemed to be targeted." ... "The spokesman said most of the dismissals were administrative and sales positions, and outside of manufacturing." This has little to do with performance or any conspiracies. If your output of products is about to dramatically shift there is no reason to think employment should remain…
Among all departments, of course not. But the job of administration and sales for the old model of car is a tremendously close match to administration and sales for the new model. If they didn't have a sufficiently large desire to fire these people, they would transfer most or all of them over.
The solarcity firings would possibly represent a shift in labor requirements, but even then they are strongly denying it with the claims of performance-based firings and not layoffs.