I just don’t know how could you be so sure of that if you didn’t visit Madagascar and observed the snakes behavior there. Here is a video that i found on YouTube of some tourists in the forests of Madagascar where they met coincidentally with the cousin of the Dumerils boa, the Madagascar ground boa which is also considered terrestrial. And guess where the boa was? High above the trees.
https://m.youtube.com/watch?v=kfpulmZ5k_A