So the minority of the WBIs are not actually X-ray machines in that they do not use X-rays. However, it's still somewhat misleading to insist that they are 'not X-ray machines' since most of the uneducated public would take that to mean that the machine doesn't depict them naked.

The whole truth in this case would be 'It doesn't use X-rays, but it still shows you without your clothes on.'