They started by identifying "left- or right-leaning" tweets. Then they decided that everything in-between were bots. Who decides what is left and what is right, and who decided that anything other than those extremes is "fake news"? There are ethical questions here.
It scares me that we now find it acceptable to classify accounts as "bots" or "Russian-backed" because of any content in the tweets, even if it's #LockHerUp or #BuildTheWall. If people really believe these things, shouldn't they be allowed to say them? What if tomorrow, something that you strongly believe in becomes labelled "fake news" or "propaganda", and your own accounts are shut down?
The methodology is flawed in the most fundamental way.
There are other technologies that can be used for detecting bots[0]. Twitter should use it.
[0] https://security.googleblog.com/2014/12/are-you-robot-introd...