No one is calling them semi-arboreal. Their feeding behavior clearly indicates that they are semi-arboreal in terms of hunting for prey. While that alone doesn't make them arboreal or even semi-arboreal, it does mean that they have successfully adapted to taking to the trees to hunt prey.
I think that in a 12" or 18" high enclosure, that a keeper (if they chose to) could safely provide for branches for them to perch on and noodle around with. A drop of less than 2' isn't going to do them a great deal of harm.