The audio engineer in me squirms at the name HDR. Did they increase the bit depth? Nah. Is the dynamic range higher? Nah. It's just a hip marketing name for a different type of on-the-fly mixing that has nothing to do with increasing the actual dynamic range. I'm shaking my fist at thee!
The term is actually an industry one.
Numerous games before us have employed an HDR mixing structure with great success. Most noteably would be the work done by DICE. It is these games and many others that paved the way for Rocket League. Typically this type of iteration happens before a game ships, but the HDR system was popularized after Rocket League's launch. Once HDR came out, we saw an opportunity to improve Rocket League!