They may have a decent number of downloads, but none of us knows how many users they have. I don't know how long the app has been on the store, but it only has 53 ratings which indicates very little engagement.
There is almost no incentive to rate app. They can't reward user and why should someone leave a comment? This is why I like what Amazon does with comment.... but if most of these are real users I think the app did a good job.