I don't know if Apple did a study, and I'm not particularly inclined to look hard for it, because the argumentation from the article series itself is pretty much bogus and uses some weird test setups (like https://www.asktog.com/SunWorldColumns/S02KeyboardVMouse3.ht... and the e -> | replacement game); that, coupled with my real-world experience which every day proves superiority of keyboard over mouse in structured interfaces, leads me to assign very low prior to the validity of the conclusion of that Apple study, as reported by Tog.

(The study perhaps had a more narrow set of conclusions than presented in the article. Wouldn't surprise me.)