Ask your doctor but that doesn't seem like a drastic drop from my experience. My eGFR fluctuates a lot, mainly due to differences in hydration. Muscle activity or atrophy can also have an effect, and my doctor has told me both blood pressure and heart ejection fraction can affect eGFR. My doc also does the Cystatin C which is more stable and generally higher.

Mountain Dew has caffeine. Is that what worried the nurses?