The FTC makes it clear saying, “A product that includes foreign components may be called ‘Assembled in USA’ without qualification when its principal assembly takes place in the U.S. and the assembly is substantial.”
FTC adds, “All the major components of a computer, including the motherboard and hard drive, are imported. The computer’s components then are put together in a simple ‘screwdriver’ operation in the U.S., are not substantially transformed under the Customs Standard, and must be marked with a foreign country of origin. An ‘Assembled in U.S.’ claim without further qualification is deceptive.” 9to5Mac notes that it is possible than an iMac assembly plant is secretly running here in the U.S.