Common guys, let's give them some credit.
They have come up with yet another cleaver way of identifying low quality sites (a.k.a. spammers/affiliates/scrapers/etc) but their implementation sucks. Obviously they don't give a s..t about messing up your stats. What they should have done is use keywords normally sent from their SERPs. Also they should have sent only few a day instead of hundreds of dumb referrals from the same IP block. This way very few people would have noticed their "quality checking". However, it seems they have chosen to cut few corners here. I think by now most of the cloakers have adopted which makes further probing kind of pointless.