Hi, Nigel,
Nigel Allan 'Montana taken with flash'
It appears that the exposure time was such that there is a blurred component from the ambient illumination (what I sometimes call an "aura").
While that can be a useful artistic tool, in most cases is just makes the image look a little vague.
Many cameras, in their Programmed Exposure mode, with flash active, will set the exposure parameters to provide "good exposure" of portions of the image not benefiting from the flash illumination. But often, they will impose an upper limit on exposure time ("lower limit on shutter speed", perhaps 1/60 sec) to avert substantial "aura".
Often in other automatic exposure control modes (such as "aperture priority") the camera will just let the exposure time fall where proper exposure of the background would dictate, often resulting in substantial aura (especially if the ambient illumination level is low).
Often control of this effect calls for fully manual exposure settings, with the aperture set , for example, where depth-of-field considerations dictate, and the shutter speed set at the highest allowed when flash is involved.