This example is always cited as different from the "demographics" approach. But it literally started by segmenting the buyers, and then focussing on a previously unrecognised demographic sector (car commuters).

Clay Christensen is smart, and one of the many things he is smart about is marketing Clay Christensen.

How is "car commuters" a demographic segment?

Does the word "demography" mean anything?

Is "people who like to buy milkshakes" a demographic segment too?

Good segmentation is mostly not by demography nowadays. At best, demographics are a correlative element to something more fundamental, usually economic, behavioural or psychographic.

> Clay Christensen is smart

Not anymore. He died in 2020.