As others have suggested, it might simply be a case of a family member of one of your neighbours saying "We'll drive to your house and leave our car there. Then we can all go together, in your car, to the airport and share the cost of parking just one car, rather than two". (If, upon their arrival, there was no free space immediately outside the home of the relevant neighbour, they would have simply parked in the nearest free space - which just happened to be outside your house).
However it only takes a few moments for the Old Bill to find out who the registered owner is, and to phone them, (as in my example above) so it could still be worth mentioning it to them.