Am guessing these ARE in fact, incendiary per 'where there is smoke fire'; but wondering if these were 'slightly' different and he was just venting. . .
Again, we need to know more; but seems little doubt, he was 'stressed'. . .and when ongoing; it can take a very bad toll; especially if he 'other' mental deterioration - known or unknown - which culminated in a most unfortunate series of events. Whatever they were just prior to his being found.
The broken floor in his kitchen another mystery???