They were assigned roles to examine the spread of information and behaviour. The agents pay tax into a chest, as decreed by the (dynamic) rules. There are agents assigned to the roles of pro- and anti-tax influencers; agents in proximity to these influencers would change their own behaviour appropriately, including voting for changes in the tax.

So yes, they didn't take on these roles organically, but no, they weren't aiming to do so: they were examining behavioral influence and community dynamics with that particular experiment.

I'd recommend skimming over the paper; it's a pretty quick read and they aren't making any truly outrageous claims IMO.