I think a lot of this is initial skill as a child + ALL THE EXPERIENCE AND REPETITIONS.
In football, for QBs and in baseball, for pitchers, I honestly just think it's a combination of the inherent tip of the bell curve of arm strength + growing up throwing wild and hard and not worrying about accuracy. Having that random, natural plus from dumb luck added with physical development that comes from years of use/recovery yields that potential for an extra strong arm (and thus, velocity).
Same with basketball, with height + coordination (uncommon combination) of the tip of the bell curve. You're tall, kid. Play basketball. A lot of basketball. Those tall kids tend to become tall adults, but even if they don't, they have all those repetitions growing up and can just play guard.
None of that is to poo-poo athletic intelligence. I just think it's a combination of natural attributes and due to those, getting tons of reps. It's not like mental IQ, where you could take a random 30 year old and they'd display giftedness in a nonverbal/quantitative test.
Except that everything you just said is effectively the opposite of what the video presented.
They are able to test specific things that relate to certain areas of cognitive ability. Not "IQ", but still measurable things related to the way your brain can ingress information, effectively process is, and make decisions, within split seconds.
If it was just initial skill and all the experience and repetitions, things like being a QB would be MUCH more correlated to physical ability than it is. And yet... Jamarcus Russell with all the measurable talent in the world flamed out, and Drew Brees, a too-short guy with a too-weak arm, had a potentially HoF career. When I heard in the video that Brees was off the charts on this test, it made perfect sense to me.
They also talked about visual tracking--again a cognitive ability. The average person in a test can track three independent visual things simultaneously. Guys who are successful at the safety position in football? Some of them are capable of tracking 8 or 9. Again that's not "IQ" but it's something unique in their brains that stands out against others.
Obviously the experience and repetitions are critically important. But I think it's quite plausible that what sets some athletes apart isn't the raw talent and the experience/reps, but an additional--measurable--difference in specific
cognitive abilities that are particularly important for sport.
