I may be wrong in your case (even though I doubt it), but that is not a behavior of a legit newbie account and instead of someone who already has some experience here and probably has a couple of accounts doing in bounty campaigns.
Well, you're not wrong though, the above post me proves it all. Btw nice catch YOSHIE, i wonder how much time it takes before you get those info but doesn't matter anyway, good job.
So, a good campaign, might help the promoters website to get a better position in Google searches
Only if the campaign runs in few months or years. But soon as it ends and participants remove the signature links, and a new cache is saved by google and crawled by googlebot, seo ranks will probably decrease. That's why these exisiting long running campaigns really benefits the most.