Update: I just went to the door to have another look at the cat and the next door neighbours head poked over the fence, having heard the meowing.
Lucky I wasn't caught in the act of unending a bucket of water

Apparently it's a new addition to their cat household, and is a rescue cat. Very friendly for a rescue! Anyway, came over the fence and then apparently got confused about where to go next, so was asking us for help in it's own way.
If it happens in the future, at least I know which fence to turf it over.