There is simple uneven surface:
Its origin point is located where 3D cursor is. Once selected edge loop is extruded its vertex normals are expected to be as a continuation of connecting edge, like:
However they are shifted and are oriented down:
If changing origin point they change their orientation. They get approximately desired orientation if origin point is snapped to 2 vertices of the edge loop not selected on the first screenshot.
Are vertex normals oriented regarding the origin point location ? How to orient vertex normals of the mesh to be oriented as a continuation of adjacent edges ? (this could be useful for some cases like scaling along normals etc.)