Refusing to hear the dogwhistles is much motivated listening as refusing to hear his condemnations of the far-right groups in that quote. Every listener has the privilege to infer the meaning and mind of their interlocutor given his utterances, and every speaker bears the responsibility of crafting their utterances to make their intended meaning understood by as clearly as possible by their audience. Yes, some listeners might interrogate an utterance in vain, looking for hidden meanings that just aren't there. But accepting the facile meaning of an utterance with total credulity is equally a losing strategy.