although if memory serves me correctly something similar happened when Yobit was running its last campaign--but it wasn't because of Yobit's scammy nature; it was because the participants were spamming the forum like crazy. It was unbelievable how many garbage posts were cranked out during that brief period when Yobit had hundreds of signature campaign participants promoting them.
It is because of what you said but also because of Yobit approach to run their signature campaign on the forum.
They did not have announcement thread about their campaign, on the forum. They run its on their website and in the first round, they opened it from Full member rank and above. Additionally, it is a paid per post campaign.
After theymos solution to ban their signature and spam participants (who were reported) a few months, they came back and kept spamming the forum. Until the take over of yahoo62278 to manage that campaign.