Yes, that study was set up to determine whether adding milk and sugar/NDC to coffee affected the kinetics of polyphenolic acid equivalents,which are of interest to some who believe they have anti-oxidant health benefits. I made the assumption that a similar effect would be observed for caffeine, which is an aromatic compound (a xanthine) but not a phenol or polyphenol. I was unable to find any actual studies on the effect of milk and NDC on caffeine pharmacokinetics, specifically the rate of absorption.

There are some claims (without experimental support) that fats (including whole milk) may slow the absorption of caffeine, such as this one:

https://paleoonthego.com/blogs/foods/5- ... -to-coffee

And of course there are plenty of well designed studies of the metabolism of caffeine that show the effects of genetic variation (cytochrome enzymes) and other factors (like smoking, EtOH consumption, and even consumption of common foods (like grapefruits and broccoli) that affect caffeine pharmacokinetics. There doesn't seem to be any easily available study like the one I referred to that specifically deals with the effects of milk/cream on caffeine absorption. But the study does suggest that NDC (and I'd also suspect high-fat milk or cream) would slow caffeine absorption.

Until that study appears, I'd say the question is still open.