I'd be inclined to agree with you, but it's hard to me to believe that all these kids went to college (or got some type of computer training) only by working with their phones/tablets.
It's not that they only use their phones/tablets, it's that the phone/tablet is the first tool they reach for, the default device, and UI conventions from that space feel correct and natural to them, just as they feel clumsy and jarring to me. (How old am I? Old enough that I still use an opto-mechnical mouse with a ball, because I still like the extra weight and inertia it has over a pure optical mouse!)