That whitepaper compares the counts of posts in a set of (arbitrarily chosen) hashtags to Instagram. All it proves is that the ratio of posts between these hashtags is different between TikTok and Instagram.

Their findings are unrelated to whether content is promoted or muted, they only look at post count. They don't even determine that it isn't Instagram that is biased (as they only compare the ratios), and these differences can pretty easily be attributed to different userbases.

They never explain how they chose hashtags that are compared, which could potentially be biased.

This isn't to say that TikTok isn't doing these things. This PDF just doesn't prove anything, and its claims are overstated.

See the discussion from this whitepaper was posted to HN at the time: https://news.ycombinator.com/item?id=38754653