Blender Model imported to unity, normals flipped wrong way work?

Hello, I just wanted to ask why this is working? I was very confused at first to why my tree animation models log section was looking distorted, then I realized I was seeing through it because of the normals, when I recalculated I could then see through the tree to the middle that wasn't see through. Flipping the normal's the opposite way in what I believe is backward seemed to have stopped the see through issue but I was more curious as to why it does since its not facing the right way?