The why is simple.
Carson is the last refuge for the people that are abandoning Bush, conservatives that dont like Trump, and the only person near Trump enough for the few supporters of the remaining candidates to latch onto and feel like they are backing someone that they think has a chance.
You're probably correct, but it's interesting that 'support' would go to Carson, and not Carly. She's closer to GOPe policies, and is way better versed on the subjects than Carson.
Leads me to believe the numbers are being manipulated to shift Trump support towards the "kinder gentler" Carson, who would later be easier to dispatch than Carly.