Hey, PGad! In the first level (private property field) you need to talk with the man in front of the house. This triggers a mini game. After you complete the mini game you need to speak with that person again. Then you open the inventory and click on the mobile phone. Finally you speak with the deminer to proceed to the second level.
The first part is like a cutscene which needs your input to move along. It's linear because it serves only to set the story and show parts of the dialog system. You will see that all the other meetings you are not resicted.