“Bokeh” simply means blur, specifically out-of-focus blur (as opposed to the kinds caused by subject or camera movement). It includes, but is not limited to, out-of-focus highlights. Out-of-focus specular highlights are simply where aperture shape will show up most easily in pictures (i.e., spots of bright sky in out-of-focus foliage, for example).
The reason people think it only refers to highlights, and that the shape of the aperture blades are the defining feature, is because that’s the most obvious effect.
Humans like obvious. The only lens I ever got rid of because of its specular highlight bokeh was a Zeiss 100mm ƒ/3.5 for the Hasselblad. It had five aperture blades, and small, bright out-of-focus spots were perfect pentagons.
