This paper presents a novel approach to open-set segmentation using large-scale point cloud data generated by LiDAR scanning of outdoor scenes. Combining existing research in object defect detection with the strengths of the Mamba architecture (which leverages long-range dependencies and excels at large-scale data scalability), we propose a reconstruction-based open-set segmentation method. This approach not only improves the performance of our own open-set segmentation method but also of existing methods. The Mamba-based architecture demonstrates competitive performance compared to existing voxel-based convolution-based methods. Our proposed approach has potential applications in diverse fields, including robotics, automotive, and land surveillance.