I don't believe he is adopting naive realism at all. Regarding subject-object, he's been very unclear on that, I'm not sure what's his take on it. Regarding metaphysics, he often speak in the metaphysical language, I believe for the sake of convenience of communication, but in many places clarified his phenomenological approach. Here is a definition of "Mind" that he gave in one of his blogs: "I use the term 'mind' in a very broad sense, not necessarily implying cognition, but just raw (potential for) experience" (meaning conscious experience of course). In one video he said that all that exists within the universe of Mind are only conscious experiences (=conscious phenomena) (I don't remember the exact wording but I believe I captured the meaning).
The problem is that we use a common language that has historically developed within the common paradigm of naive realism and subject-object dualism. Every sentence in our language follows the subject–verb–object structure. We don't have a special language to use for discussing anything beyond such paradigm. So, when for example BK says "a chair", what he means is ideations of a "chair" (=conscious phenomena) in MAL that excite corresponding sense perceptions of a "chair" (=conscious phenomena) in human minds. But his listeners, following habitual cognitive patterns of naive realism and subject-object dualism, will more often interpret it as if he is talking about an object of a "chair" existing in the "external world out there" (=abstraction) perceived by a subject "me" (another abstraction). Same situation happens when he talks about the MAL itself. This is inevitable, but at least it's a step on the path towards disentanglement from the patterns of naive realism and subject-object dualism, which usually takes a long time because there are so many layers of cognitive distorted dualistic perception/interpretation of reality do disentangle from.