Post author here: this post was written in June 2017, and the subject has become increasingly relevant since the MySpace video advertising bot fraud reported by BuzzFeed on October 27, 2017:
https://www.buzzfeed.com/craigsilverman/remember-tom
The conclusion that Facebook has bots other than Facebot is interesting. I wonder if Scott was able to identify how many problematic user agent strings were on Facebook's network.