This is the reason, why I always try to show untextured meshes. The texture can hide a lot of defects.

The problem is not in the exporting, but in the image taking! The model has many unicolor areas, which makes it very hard for the software to reconstruct those. You either have to use chalk/scanning spray or use some other method to create enough surface features. This is key to successful photogrammetry.

Please see the example images at www.openscan.eu/scan-gallery