What's going on here? The paper doesn't say, but the key thing to note is that the neural network is only attempting to identify rules that work (i.e., build near a river). It doesn't actually care how those rules are conveyed—it simply associates text with a random action and determines whether the results are any good. If it's lucky, it can end up associating a useful rule with a random bit of text. It has a better chance of doing so with nonrandom bits of text like the owner's manual, but it can still provide useful guidance no matter what it's given to work with.