The practice of ... clicking on an advertisement hosted on a website with the intention of ... draining revenue from the advertiser
Elsewhere on the same page they've even gone to the extent of explaining how they calculate the average revenue they think each simulated click drains from the entities they wish to "resist"
In AdNauseum's implementation, the revenue is drained from the advertisers to all of the sites where those ads are hosted and where AdNauseum's users browse. Neither AdNauseum nor the users browsing the sites benefit from that revenue. Instead, the advertiser's marketing budget is slightly less effective.
This changes the behavior from an intent to profit to an intent to harm. I'm certain that they could prove in court that they do not intend to profit from this activity. But I don't know whether or not the court would classify the outcome of the activity as "resistance" or "harm".