I haven't read the article, but just wanted to chime in that there is some correlation between sensitivity and giftedness (to the point where it is not unusual for gifted kids to have sensory processing disorder). That sensitivity can be apparent in infancy as fussiness. And I agree that it may all go back to a hypersensitive nervous system.
My DD7 was a super-sensitive baby and last year did OT for SPD. Looking back, I don't know how I survived LOL. (and of course all the while my mother blamed me - she thought I was too anxious about my first baby - gee thanks mom. but she was born that way.) Now that I have four boys in addition to her, and I look back at their various temperments, I think they're all pretty smart but it's too early for me to compare levels. My easiest, happiest baby, DS2 (who seems even now to be the happiest baby who ever lived LOL, if only just by comparison - it's his fault we ended up having one more after him) seems to be brighter than the other kids because none of the others were talking at his age (the others are late bloomers/2E-types; whereas happy boy was the most healthy of my pgs due to some issues I have). And the latest one, DS(3 months), is pretty darn sensitive to sound (like my bare feet tiptoe-ing on the carpet) for a kid growing up in such a noisy household. Only time will tell.
I think the only thing to be gleaned from this information is that when dealing with a fussy baby we may look on the bright side - he/she might turn out to be gifted. A silver lining amidst the crying.
