While it may provide a comforting myth to believe that "market" is in some way inherently "smartphones as a whole", or "personal computers as a whole", and therefore by definition it is impossible for Apple to be a "monopolist" - that's really just the same logic that says "America waterboards prisoners, America doesn't torture, therefore Waterboarding isn't torture".
The more complex truth is that "market" as a definition has been developing in multiple cases, both in America, and internationally. Increasingly, it is being defined more narrowly, such that iOS itself is a market, within which Apple will face increasing scrutiny over their actions to prevent developers from using competitors to Apple's own offerings for App download hosting, and payment transaction processing.