So I was playing the Cities & Knights scenario in the Catan app. On my turn, I rolled a seven. I moved the robber on the mountains hex where both of my opponents have a settlement and a city adjacent to it, as shown in the photo.
After I did that, the red player's settlement lights up, meaning I can steal from him. What I don't understand is, why did the green city not light up? I know that a city with a city wall adds 2 extra cards to your card limit, but I'm not quite sure that it also protects your cards when a player moves the robber on a hex adjacent to your walled city?