I'm not sure, though I am inclined to believe what they say. We aren't any other animal but humans, so we've no way of knowing why any animal would do what they do. "Natural" behaviour can be anything from innate response to external stimulus or a learned response based on some past events. A human being can respond in some way to a certain stimulus, say, get worried when a loved one isn't home by night. An animal may or may not respond in the same way. After all, in the animal world anyone can get eaten anytime and they have no time to sit up and wait...