Look at Huntsman's total as "static". The poll didn't force anybody to make a specific selection. Therefore, it's actually a laundry list of everybody that the respondent would be willing to support.
Those who checked Huntsman were essentially checking "all of the above".
All of which makes the even lower totals for Bush and Christie even more damning...
It is not 29% out of 100%.
I agree with you, but I think it has to be the case that many poll participants don't know who Huntsman is. I'd almost vote for Hillary in a presidential race against Huntsman.