Carson definitely has lower name recognition than everyone else on that list, so it's possible he could be functioning as "generic Republican".
That's not how name recognition normally works though. Typically, low name recognition means low support in polls, whereas "Generic Democrat" and "Generic Republican" tend to poll pretty well.
I'm inclined to think it's just a bad poll. But I'd like to see other pollsters include Carson in GE matchups, and/or poll his name recognition before jumping to conclusions.
