A friend who studied engineering at MIT made a similar distinction, and it's where I expected the article to go, being hosted there.

The notion was that the development of engines, as opposed to simpler motors and mechanical systems, had required a net set of skills that led to a recognizably different discipline. More systematic, more concerned with dynamics and feedbacks, cross-disciplinary to materials and machining techniques, more data driven, more advanced mathematic and analytic techniques in support of these. The sense was simpler mechanical systems were more linear and engines were highly non-linear, and required a different mindset to approach.

I like the distinction and appreciate the different terms.