That's the Ask Tog "study"[1]. It wasn't programmers, just regular users. The problem is he just says it, and of course Apple at the time of the Macintosh's development would have a strong motivation to prove mousing superior to keyboarding to skeptical users. Additionally, the experience level of the users was never specified.

[1]: https://www.asktog.com/TOI/toi06KeyboardVMouse1.html