Earlier quoted context omitted.
Yes, that's how stimulants work. The first hit, after abstinence, is always the best.
Well obviously, the study could be bunk, but decaf essentially contains no stimulant, so this isn't really enough to explain the results.
I have been experimenting with reducing/abstaining from coffee and I am well aware of its effects, and I doubt you can reach very strong conclusions. There are times where I have experienced no headaches during my abstinence week, others where I've felt terribly, this last one during the heatwave I actually felt pretty good staying away from coffee, and I have been enjoying the slower pace of my thought.
Nutritional research is, as always, as rigorous as astrology.
Personally, coffee makes me much more anxious, more impulsive, more able to bruteforce through things I hate, but reduces creativity and contemplation; just like amfetamine BTW.