XnView can support the DICOM format for a longer time, now. The file extensions are .dcm, .acr, .dc3, and .dicom.
I've downloaded your DICOM file to check but displaying thumbnails or opening it failed:
Your DICOM file has no file extension, so with default settings XnView will not be able to recognize the file format unless you deactive setting "Recognize only by extension" (in Tools > Options | Browser > File list | "Misc" tab).
After unchecking the setting "Recognize only by extension" a thumbnail is displayed and I could open the DICOM image, but it didn't look right (bottom part is just black, top part looks like a random mix of black and white pixel):
Perhaps a variation of DICOM format that isn't supported by XnView, yet?