  During Australia's unprecedented bushfires in 2019-2020, misinformation
blaming arson resurfaced on Twitter using #ArsonEmergency. The extent to which
bots were responsible for disseminating and amplifying this misinformation has
received scrutiny in the media and academic research. Here we study Twitter
communities spreading this misinformation during the population-level event,
and investigate the role of online communities and bots. Our in-depth
investigation of the dynamics of the discussion uses a phased approach --
before and after reporting of bots promoting the hashtag was broadcast by the
mainstream media. Though we did not find many bots, the most bot-like accounts
were social bots, which present as genuine humans. Further, we distilled
meaningful quantitative differences between two polarised communities in the
Twitter discussion, resulting in the following insights. First, Supporters of
the arson narrative promoted misinformation by engaging others directly with
replies and mentions using hashtags and links to external sources. In response,
Opposers retweeted fact-based articles and official information. Second,
Supporters were embedded throughout their interaction networks, but Opposers
obtained high centrality more efficiently despite their peripheral positions.
By the last phase, Opposers and unaffiliated accounts appeared to coordinate,
potentially reaching a broader audience. Finally, unaffiliated accounts shared
the same URLs as Opposers over Supporters by a ratio of 9:1 in the last phase,
having shared mostly Supporter URLs in the first phase. This foiled Supporters'
efforts, highlighting the value of exposing misinformation campaigns. We
speculate that the communication strategies observed here could be discoverable
in other misinformation-related discussions and could inform
counter-strategies.
