It's been interesting to watch this story unfold. Twitter is a broadcast system and therefore has many (useful [and not useful]) bots. These aren't users, but not all of them are spam. It's a simple counter-example to show that simple user (and engagement) counts will almost certainly be misleading. Twitter is in a big-time catch 22 with reporting here. It'll take skill to report a qualitative aspect like engagement with a quantitative metric (like they're expected to).