They used the equivalent of the thumb system. Many people give 5 stars, or 1 star. There are some that give in between. Many places consider anything less than 5 star to mean there was a problem (Uber, Amazon, reviews for phone support).
No, it's anecdata. A lot of stuff I see tends to have a large amount of 5s and 1s. There is often 2-4s, but the amount is very often less than 5s or 1s.
It's mostly just looking at trends. A few things I've purchased from Amazon come with a little advertising slip that says "if this product is anything less than 5 stars, let us know what we can do to make it better!" I've seen plenty of stories from people complaining that their less than 5 star reviews got removed for X reason (often because it's "dishonest").
Maybe that'll be my next learning exercise: scraping the count of reviews from Amazon to support this hypothesis.
It might be that people are less motivated to take the effort to rate something if it was "meh, okay" -- whereas a 1 or 5 star rating is something you might want others to know about, so they can see/avoid the show.
