Do the Great Wall’s battlements really face inward?

That claim is too broad. The Great Wall is a network built and altered over a long period, not one identical structure. Many sections were meant to defend the frontier from threats approaching from outside, and their defensive features generally make sense in that setting. A photo without a clear sense of the terrain and direction can make the layout easy to misread.

Also, battlements are not a reliable shortcut for deciding which side was considered “inside.” Some sections have defenses along both edges, and the wall’s route and local landscape affect how each stretch is arranged. So a south-facing parapet in one place would not show that the whole wall was built the wrong way around.