No, it's all about bit errors and error correction. Highly concentrated radiation is more likely to cause multiple errors to a particular DNA strand, which can defeat the error correction and cause a mutation.
The same radiation distributed through the body will cause fewer errors per strand and be corrected.
It's been a long time since I studied dosimetry, but I was under the impression this was only significant at high doses. Do you have evidence otherwise?
The key issue is the actual wavelength being used. I have yet to see this number published. If you knew the wavelength of the X-ray then you could attain a good estimate of the radiation dose. It is well established that X-rays cause protein damage (in vitro) at 1-1.5 Angstroms which is certainly smaller than what is being used in the is case. The wavelength at which radiation damage does not occur would be interesting to determine.
The same radiation distributed through the body will cause fewer errors per strand and be corrected.