Not sure if the question is answered, but for OP's original question of whether or not BDXL (100GB Quad layer discs) are UHD Blu-rays, the simple answer is:
No, it's not.
Blu-Ray and UHD Blu-ray are not the same format, the former is 25GB per layer, the latter is approx 33GB per layer, so the latter is completely incompatible with the former, so you will need a BR drive that specifically supports UHD Blu-ray for it.
I have NO idea why they STILL call it blu-ray, since it's an entirely different format, and the fact they are incompatible.