The reasoning is classic in its clarity. If God does not exist, Kirilov is god. If God does not exist, Kirilov must kill himself. Kirilov must therefore kill himself to become god. That logic is absurd, but it is what is needed.
Because, as we know, almost anything can be read into any book if you are determined enough. This will be especially impressed on anyone who has written fantastic fiction. He will find reviewers, both favourable and hostile, reading into his stories all manner of allegorical meanings which he never intended. (Some of the allegories thus imposed on my own books have been so ingenious and interesting that I often wish I had thought of them myself.)