That's quite a lot of conjecture about the mechanisms behind what is observed in the research, but how far do the research findings themselves take us? For example, I've read about how spaced repetition affects verbal and visual recall tasks, but has its effect on motor coordination been studied at all? It's a big leap to generalize from verbal and visual recall tasks to motor coordination tasks, yet here we have an article about a researcher who studies recall of telephone numbers and such, and the article blithely advises readers to apply his research results to learning a tennis stroke. That's a terrible application of science.

I could be wrong, but the article only mentions research on recall. The conclusions reported by the article match research results on recall. The article features one researcher, who happens to study recall. Now, if you think it's common sense that research on recall says little or nothing about hitting tennis balls or dancing the Viennese waltz, then how are you supposed to read the article? Science writing elides a lot for the sake of brevity and breeziness, but I have a hard time trusting that the author knew about research justifying the same conclusions in the case of tennis and dancing and decided that instead of mentioning how broadly the findings had been confirmed, he would lead his readers to believe that it's all based on one narrow path of research. (Also, I don't think it's a very good defense of science writing to say that an author didn't make a mistake in reasoning, he only encouraged his readers to do so.)