I thought the basketball coach analogy was a bit retarted... Cave diving isn't a spectator sport where you can armchair coach people after seeing it live, seeing it from several different angles, zoomed in, slo-mo, etc.
The word is "retarded," generally used to identify people with significant identified learning disabilities. It is usually considered to be an impolite term to use in polite conversation, akin to a racial slur.
It doesn't matter whether it is basketball, dancing, drawing, chess, or anything else that can be taught. The concept is that it is very possible for someone with good skills and great coaching/teaching ability to do a better job teaching those skills than someone who has excellent skills but a lesser ability to teach them.
Interestingly enough, you will find people in education who disagree. As a part of a study I conducted for one of the nation's largest school districts, we surveyed the opinions of teachers who had had extremely different student performances after a common assessment. Of the teachers whose students had universally failed the assessment, 100% said emphatically that teacher instructional skill had nothing to do with student achievement. In contrast, 100% of the teachers whose students had universally passed the assessment with high scores said that teacher instructional decisions were the primary factor in student success. These were all heterogeneous classes--all teachers in the study had students of random ability.