Someone who denies dualism can consistently affirm the obvious truth that each of us has subjective experiences. These are different issues altogether. In fact, I don’t know of any non-dualist who denies that people have subjective experiences. Not even the more radical behaviorists went to that extreme.
Wittgenstein’s remarks in this section (Part II, Section V) of the Philosophical Investigations do not ostensibly advance a philosophical behaviorism. At most, his remarks raise interesting questions about some of the assumptions of the dualist regarding our talk about behavior and our talk about mental states. The argument that he makes is one that, if successful, undermines some important premises of the dualist thesis.