The man was hallucinating and talking about zombies, and was shot by the homeowner.
The article poses the possibility that the man was on drugs, which he may have been. I’m guessing he was experiencing the throes of psychosis due to an underlying illness, though that doesn’t preclude drugs in his system. People who are suffering from a mental illness may very well self-medicate.
I don’t blame the homeowners for defending their home. They had ever right to do so and I would have likely done the same in this context. Having said that, people with illnesses like schizophrenia pose the greatest danger to themselves, not others.
Again, this is all speculative on my part, but it makes sense.