I don't know why everyone thinks that getting an app featured by Apple is some sort of huge conspiracy. If an app is of high quality and has some traction, it's not absurd for it to gain positive attention from Apple.
In the case of Halftone, the quality of the app is excellent and has significant usage. There are 1100+ reviews that average to 4.5 stars. These numbers would be considered fantastic by any developer's standards.
In 2010 I had a free app featured that had no previous traction. At the time, the app had been in the Appstore for about three weeks, and my second update just been made available. Total downloads before being featured were under 20. To me, being featured seemed to be a random event.
Apple often features apps of poor quality and it's not always clear why (e.g. games with 3 stars developed by big names or indie apps not working as they promise). So, yes, I understand why people are surprised.
You are considering the inverse of the matter. The post is about a high quality app being featured. My comment was intended to say that it shouldn't be surprising when a quality app is featured.
But maybe all these reviews and downloads came after getting featured by Apple. I surely believe that your App will be downloaded a lot more times if you are highlighted by Apple and being highlighted by Apple could mean to people "that the App is definitive worth it and good" and so they probably more likely to give good ratings.
I'm sure there was some spike in downloads because of the feature, however, it wouldn't be more than a few thousand. This isn't very significant considering that Halftone probably has over 100K downloads (extrapolating from the assumption that 1% of downloaders submit a review). Of course this is a very rough estimation, but I think it puts Halftone's traction into perspective.
In the case of Halftone, the quality of the app is excellent and has significant usage. There are 1100+ reviews that average to 4.5 stars. These numbers would be considered fantastic by any developer's standards.