I believe the "different texture" to be an artifact of the jpg compression. In areas with fewer details (caused by the vanishing of the shadows) the block sizes on which the jpg compression operates become larger. The different texture is a natural consequence of the varying information content with any lossy compression algorithm.
That is the most likely explanation. Compression is quite high on these web images. Also IF there was a loss of detail in one area because of a small lens contamination the compression will amplify the effect which saves bytes.