Earlier quoted context omitted.
It seems a convenient shorthand. Intelligence is surely a multi-dimensional vector, but it’s convenient in a lot of circumstances to talk about its magnitude. “All models are wrong; some models are useful.”
> Intelligence is surely a multi-dimensional vector There's a single component responsible for almost half of the difference: https://en.m.wikipedia.org/wiki/G_factor_(psychometrics)
>It is a variable that summarizes positive correlations among different cognitive tasks, reflecting the fact that an individual's performance on one type of cognitive task tends to be comparable to that person's performance on other kinds of cognitive tasks.