OK OK I found out exactly kinda
So, you can do it either jamming your thumb really bad, like shoving it into the snow when you fall. Or, when you are holdin onto your poll, when you fall on your thumb, or you try to release from your poll but the poll stays around the palm area. The best way to have it not happen is to be able to lose your pole completely and fall on your palm. The only probelm with this is that someone like me will be doin a lot of hikin to get their poll.