This seems pretty clear. He had a bad experience but didn't leave a review for the place, and then when the review period expired, he saw that the place had left a bad review for him. Airbnb keeps both users blind to each other's reviews until the review period has expired, because otherwise people will use the threat of leaving a bad review (as retribution) in order to ensure they get reviewed well. But he did an end-run around this and posted reviews on multiple other sites, which makes airbnb's system break down.

It sounds like Airbnb just needs a way for people to respond to reviews that are left for them. I'm surprised it doesn't have that already.