I have had this happen, but worse:
a) all categories 5 stars, except for one with 4.
b) overall rating? 3 stars (three)!!!
I asked the Guest for feedback, who kindly entered into a conversation with me. It turns out he found my listing as expected in all categories, the descriptions accurate, and the photographs clear and not at all missleading. Why the 3 star rating? Because I have a modest home and the room is relatively small (even though I described the dimensions, etc.). For him a 5-star rating is what a luxury room would receive!
AirBnB HAS TO DO something to clarify to the Guests what the star scores mean! They put tons of effort and investment into raising the bar of hospitality, and I don't see much on an effort supporting the Hosts in getting the recognition they deserve (e.g. ensuring they receive a fair rating by putting everybody on the same page.)