It's laughable that they even call it HDR Rendering because it's definitely not "dynamic". For those that don't know HDR Lighting = High Dynamic Rendering Lighting.
You're confused about the terminology. HDR stands for "High Dynamic Range." In this case, dynamic range is referring to the difference between the maximum and minimum values possible for a parameter, which in this case is luminance. It sounds like you're using it to mean "changing on the fly," which it doesn't.