Other way around.
Newer technology to old. Since HID bi-xenon projectors are newer it's labeled a retrofit.
Ever heard someone talking about a classic or older car, "The A/C was retrofitted with 134a"
Meaning it was R12 and now the newer 134a.
But I see what you did there, you took the root word "retro" meaning older style and "fit" meaning adapted and combined them resulting in "old style adapted" which implies new adapted to old. Make sense? Probably not!
Ah yes! The english language, unlike the metric system, it doesn't make sense.