I mean how do you know that they are boosting them ? We don't even know what criteria they are using for the rankings.
I am happy to call them out but just from the screenshot there is no indicator to me they are biased towards specifically Reddit app.
2.8 is super low for ratings. So if that is a boosted one it is a really bad effort.
Selection bias in app store. This is done by obscuring older reviews under the excuse of the app being a different version. You're then creating a selection of what gets through, and this happens to usually work in favour of the apps. And it's particularly true for Reddit app. In the past a lot of people tried it, found a clusterfuck, rated it badly and moved to other apps, never looking back. And those are the types of reviews that got buried.
It wouldn't surprise me if reddit apps got below 2.8. That's just their quality level.