I think they assume that a USA device would have tariff only on the imported chips inside, whereas a device from another country would have its chips tariffed, as well as an additional tariff on the full device when imported.

I don’t know if this is the case or not because Trump is unclear and as others have pointed out this would be trivial to evade if components aren’t tariffed separately.

No matter what those in the USA would be paying more for electronics.