We usually assume that there is law in a society only if that society has its... laws. But I would like to ask if you think there is another important sense of "law" or of "legal matters" (I'm a law student). Suppose Pete goes to some wise and strong person, Justine, and tells her: "I want that guy, Pat, to be forced to give me back the tool I lent him, since the time has passed when he sould give it back to me, according to what we agreed." As far as I see it, if Justine wants to hear Pete and Pat and have some intervention in their dispute, she has a legal question in hands. She will be like a judge. I think that some questions are legal irrespective of whether some group of people has any previous legal organization. This story between Pete, Pat and Justine could take place on a desert island where the three might have just arrived coming from different places.
As you say, Justine would be "like" a judge, but I don't think that actually makes her a the sort of judge who presides over a court of law. She might be making a moral judgment or even a political judgment. Clearly, ideas like what one "should" and should not do are operant here, and clearly it seems to be relevant to appeal to reasons, such as the agreement Pete and Pat made. But those are also the sort of things to which friends or students or romantic partners appeal in disputes. You don't have, however, a formalized legal code. Procedures for adjudication and appeal. Etc. So, while I'd say you have some of the elements of the rule of law or legal institutions, what you describe isn't quite sufficient to warrant describing their situation as "legal."