your questions regarding the game rules (improving the interpretation).

Basically, until the Grand Order (GO) is breached, it is forbidden for him to move around the treasure area in any way. Since the Monarchs are the only GO in the passage, he is even forbidden to fly over them and breach them from the sand.
Mountains are not part of the treasure area, so his shortest path was through the mountains, as I show in the screenshot.
According to the current rules, the interpretation of permissible actions should be exactly like this. The lawyer explained everything correctly.