Proof - as if it were needed - that Airbnb's ratings and review system is not fit for purpose. I wonder how many of those hosts gave the guest a 5* review, not based on his/her true worth as a guest, but simply because they were hoping the guest would reciprocate.
It's only a matter of time until the ability to review guests is taken away from us anyway. The vast majority of guests hate being reviewed - the way they see it (understandably), is that they're paying good money for a nice trip away, so why should they have to stress about what a neurotic or pernickety host might have to say about them in a public review on the internet? (And let's face it, some hosts go way over the top in complaining about the tiniest of guest "transgressions")
Quite simply, hosts reviewing guests is yet another barrier to maximising bookings, and in the run up to going public, Airbnb are already eliminating those barriers, one by one. Shouldn't be long now until mysterious "glitches" start preventing hosts from leaving negative reviews of their most troublesome guests.