You are right, the speed limit is 50, my bad. I just started using the app StreetComplete, a gamified OpenStreetMap app. When I tried to choose there was no sign, it seemed to me the app wanted to suggest no speed limit, and then I tried the zone button, but then it gave me 30 as the default and I did not understand I could edit that directly. Once a quest is complete, the app does not allow you to edit (?), so I guess I need to find a way to edit any mistakes I have made in here.