If so, then this was not some component or process that might randomly corrupt bits (e.g. memory cards, hard drives, motherboards, cables, etc.). Instead, this was some component that was aware of the format of the image files, such as the camera, image processing software, etc. I don't know the CR2 file format, but it is also logically possible that simple file truncation might cause this effect for some file formats. In this case, it would be some component or process that was able to preserve the integrity of the file system, but change the file lengths, such software that moves files between locations, etc.
I believe that CR2 is variable length compressed. That being the case, it is pretty hard to predict the visual effects of file corruption.