Just a small disclaimer that I in no way think this is true, it's just a fun way to think about the game. My thoughts on this are that the zombies are hallucinations the protagonist experiences, or altered perceptions of real people. They bring him fear so he is too scared to leave his house. Crazy Dave is somebody also undergoing therapy, or at least somebody who understands your condition, and either helps you cope with the hallucinations with his "help", or takes part due to his own mental health issues. Where the plants come in is as part of the therapy. The protagonist has been provided with gardening tools, and gardening is part of his therapy to give back to the community or even j...