I think Brando liked to dick with people who asked him about his technique. You hear so many of these tales where he deprecates his ability; maybe he was saying those things to brush off questioners so he could keep his process private.
For example, watch his work in “Last Tango in Paris“, at his wife’s casket, where he goes from yelling to sobbing. Looking at the editing, you can see there is no way they could have cut away. He made that transition from furious to bereft using something inside himself. Yet you also read an interview where he claims that he rubbed onion into his eyes for that scene.
Brando just didn’t want to give away his acting power by revealing his technique, so he made up these stories of non-acting so the interviewer would stop probing.