Where in your video does it say that?Its not using any height data from lidar or whatever, its just 'guessing' a height mesh from 2d images.
Thus it could of seen these stains and its algorithm thought Oh that looks like a plane thus lets create a plane heightmesh here
Your video explains that Google uses photogrammetry, which uses several images of the same object to determine its location in space.
A special case, called stereophotogrammetry, involves estimating the three-dimensional coordinates of points on an object employing measurements made in two or more photographic images taken from different positions (see stereoscopy). Common points are identified on each image. A line of sight (or ray) can be constructed from the camera location to the point on the object. It is the intersection of these rays (triangulation) that determines the three-dimensional location of the point.
For more details, see Wikipedia.