This is a different definition of a functor, i.e., not in the category theory sense of the word, hence: “not to be confused with the functor concept in category theory”.
1. A racket is something you hit balls with.
2. A racket is a lot of loud noise.
Racket in 1 and 2 sound the same, and are spelled the same, but mean totally different things.
The same holds true for the Apache Commons “functor”, which is referring to the same usage as the wikipedia version.