Wheels are universally measured in inches. Metric wheels were experimented with in the 80's and 90's, with little success.
Do you really think your 7.5Jx17 wheels are unique to the UK (they don't have a metric size cast into them), or that our tyres (which don't have a metric dia marked on them) are only used here?
Tyre width in metric but dia in imperial is the universal standard.
Aside from anything else I think the tyre size was visible in the photo.
I am sure most 16" wheels wouldn't fit but some motorsport wheels are built with a lot of brake clearance in mind.