Your son made a lucky guess: that family could have been from New Zealand or South Africa or a number of other places that have left-hand drive. (Probably not Great Britain or Ireland, though–the sun-tan in winter rules that out.)
Yep, pretty lame. How about British Virgin Islands, Bermuda, or India. 
Thailand is another.
And we shouldn’t completely rule out northern hemisphere countries. When I lived in the ski country of northwestern Colorado, from time to time I got a sun tan on my left arm from driving my Ford truck with the window open. Even in the winter, and esp in the early spring there are occasionally afternoons warm enough to leave the window down when tooling about town, and the sun’s reflection off the snow banks can produce a powerful burn.