Cars Toons is a series of American computer-animated short films by Pixar. It features Lightning McQueen and Mater from "Cars". Larry the Cable Guy reprises his role as Mater while Keith Ferguson replaces Owen Wilson as Lightning McQueen (until "The Radiator Springs 500 ½" when Wilson reprises his role).
Keith Ferguson did not provide the voice for Lightning McQueen in "The Radiator Springs 500 ½" 
The context explains that Owen Wilson provided Lightning McQueen's voice in "The Radiator Springs 500 ½," although Keith Ferguson had been voicing McQueen in the short films prior to that. The system was likely confused because the context states that Keith Ferguson took over for Wilson for the short films, with that case being the only exception where he did not.