The change isn't necessary but I do think the scene serves a storytelling point here. It simultaneously shows the reader
a) the Chief's creepy talent for psychoanalysis and manipulation. He sees right through Mento's ruse and works out exactly why he does it, then uses the knowledge to further break Mento down and make him more malleable to his manipulation.
b) insight into Mento's personality, in that he's the sort of person who would choose to perpetuate this kind of ruse.
Plus, the idea that he pretends he can't read minds all the time because he knows it'd freak out his Fortune 500 peers ties into one of the undercurrents of the Doom Patrol concept, namely that they're the freaks and weirdos of the superhero set.