The term bot comes from social media when automated scripts would run to pollute a discussion, especially based on keywords. It has been expanded to mean insincere participation in a discussion threads, especially from commercial or government funded message farms. There's a huge amount of research on this related to Twitter if you are interested. Google "twitter misinformation bots" and I'm sure you'll find lots of it.
It is difficult for us end-users to prove anything about bots and their behavior, especially on individual posts, unless it’s glaringly obvious, like "I found a place that lets you print free money and I wanted to share the URL with you..."
Observing the forums over time however you can get a good sense of the shift to bot-ness.