I can vouch that this exact scenario has happened to one of my small businesses. Multiple reviews from actual customers are filtered out, but a negative review from someone who has never interacted with our organization is displayed normally.
We can pick apart Yelp's model and likely should, but it does appear to discount "drive-by" Yelpers who only sign up to give a good review to a single business.
This is a classic 'Yelp' business practice and many business owners you can talk to will have many of such reports.