When people say "athleticism" they usually mean blocks, dunks, running fast, and being flashy. Athleticism never means a guy hitting 90 out of 100 free throws, or having no problem hitting a three perfectly with a hand in a face, or making a perfect pass at the perfect moment, or getting in the passing lane at the exact instant needed.
Larry Bird stealing the inbounds pass from Isaiah Thomas and getting it to DJ for the layup is a thousand times more athletic than anything I ever saw Vince Carter do.
There is definitely a difference between being a great "athlete," in the sense of being a competitor in an athletic endeavor, and having great measurable athleticism in the way that term is used to evaluate professional athletes.
"Athleticism" in the professional sports context tends to denote things that are mostly inherent, as opposed to qualities that can be trained or developed through hard work and practice. Burst, agility, vertical jump, and so on.
It is definitely counter-intuitive that things like strength, endurance, and coordination don't typically get included.
I think the idea is that while Larry Bird was an amazing athlete and competitor, he didn't have the same kind of God-given physical gifts that a player like Vince Carter had. Of course, Larry Bird probably was far more "gifted" in terms of mental focus, coordination, dexterity, court vision, determination, and so on. We like to tell ourselves that those things are entirely self-determined, though.
One thing at play here is that white athletes have a tendency to be credited for their "self-earned" qualities, while black athletes tend to be talked about in terms of their "natural gifts."