Maybe he had a “No Solicitors” sign on his door.
I too would like to see more, but I’ll bet that it’s as simple as he already has his gun out when he answers the door, and this is the first knock on the door in some time.
Or maybe this is just a paranoid nut.
I suspect that he is a clinical paranoid, without a peephole or other way to see who was knocking, and so frightened that he assumed anyone at his door would be there to “get him”.
The interesting note was that he was arrested without incident. This suggests that he was not so far gone that he didn’t realize what he had done.
The alternative might be that he was half-expecting someone to come after him, suggesting involvement in the drug trade. So after hastily flushing the evidence, he peacefully surrendered to avoid a much worse sentence, figuring he could apologize down to a misdemeanor or even time served.