When the image is read from a stream it has no clue about the original file. This means it cannot determine when the image was created and it will use the current time. But I don't understand why the following code works though:
It appears that the image has exif information but not exif profile. I will take another look at it this weekend.
using (MagickImage image = new MagickImage(@"d:\caspian.tif")) { var dateTimeOriginal = image.GetAttribute("exif:DateTimeOriginal"); }