The missing, bottom half of the sphere is an integral part of the structure, and is simulated by the mass of the part you do build, in relation to gravity, which holds the base of the dome flat to the earth, without anchors.
If you can constrain the base perimeter to hold its shape, by any manner of coercion, the dome will remain integral. So you can tie it down (with ground stakes) or to cement footings -- or just rely on the weight of the dome itself, pressing down evenly, to do it.
A scale model built from PVC pipe (with non-rigid hubs) makes this pretty obvious. It really is a tensegrity, and acts just like one, given the right amount of play in the system. It will fold in, easily, at the base, if it is not rigid enough at the hubs.
Making hubs rigid masks a lot of engineering flaws, but they're still lurking. That said, the hammered-flat-EMT-ends method of hubbing is fairly proven, in light applications for shelters. For hanging, I don't know; I think the strongest node is the (near) zenith node in this type of dome.
So the 'Bat' style hanging (from a single point of suspension) might work better, as a singleton-occupant structure, from excessively light materials.
Everybody else probably overbuilds, or carefully compares accounts from built domes, and takes reasonable chances (probably, of non-catastrophic failure that leads to redesign, and more expense).
The Scouts probably saved time and money (and maybe weight) with their design, by overdesigning it the first time, which kinda sounds like what they did (pics: it did happen!)
I like that.