Obviously. However, it is an appropriate example if your goal is to teach the intricacies of the C language. You're right that if you provide such an example this early, it could perhaps use some additional commentary.

Not only is that confusingly cutesy, but largeA[i] is a double.

That was the point of the exercise: !! is an idiom to convert to boolean (which happen to be integral in C) and something a C programmer (or JavaScript programmer, for that matter) should be familiar with.

This is flatly untrue on x86 and I suspect many other architectures.

Agreed.