簡易なライトプローブ補間が使用されています。
If baked light probes are present in the Scene, an interpolated light probe will be calculated for this object and set as built-in shader uniform variables. Surface shaders use this information automatically. To add light probe contribution to your custom non-surface shaders, use ShadeSH9(worldSpaceNormal) in your vertex or pixel shader.
Additional resources: Light Probes.