The only concern I have is the way the experiment is conducted. The correct way to collect data would be to consume the Streaming API to collect the random sample of tweets provided by Twitter [0]. They should then run their algorithm to compare how they are doing against Twitter's algorithm. Currently, they are filtering out certain topics of interest and just comparing these topics. Therefore, they are filtering a great degree of noise which is actually observed by Twitter.
[0] https://dev.twitter.com/docs/api/1.1/get/statuses/sample