Assuming that someone who has read much Jack London and knows about his life would come to the same conclusions as you regarding his expertise on the matter is an easy trap to fall into.
Two philosophers were crossing a bridge over a koi pond. One pointed to two fish swimming in the pond and remarked: "Boy, those are some happy fish." The other replied: "You, not being a fish, don't know whether they are happy or not." The first said: "You, not being me, don't know whether I know they are happy or not."