Your body forms a tripod on the bike, but the bike still only has two points of contact with the ground. I've never had a low speed stability problem with mine, but maybe it's the combination of the geometry and the individual?
The Radrunner has two entirely different geometries. In almost all the youtube videos, riders demonstrating Radrunners, including the CEO, ride them as scooters, with the seat about 30" high. A man's shoulder would be about 10" higher than the bars, making a stable tripod. My seat is at 40", typical of a man's bicycle, so I can pedal. That tripod was horribly unstable.
About 1970, I met a biker whose friend had lengthened the frame of a BMW R-60 to accommodate a VW engine. Dressed in leather, he'd accelerated to 100 mph when violent wobbling threw him off. I don't think he was hospitalized, but he broke at least one bone in tumbling. Left with two points of contact and no destabilizing load, the bike straightened out and coasted down the road almost to a stop before tipping onto its cylinder heads, undamaged.
Ideally, hand grips should be even with the steering axis. When one hand moves forward, the other moves back, and your upper body stays in position relative to the bike. His bars swept back to accommodate the long frame. Steering left entailed moving both handgrips right. With two points swinging together from side to side, the tripod supporting his upper body was no longer stable.
By the time he hit 100 mph, a slight correction to the left would cause inertia to throw his shoulders right, turning the bars farther left until the bike corrected itself, throwing his shoulders right and building up to violent oscillations. On a poorly set-up bicycle, that kind of thing can occur coasting down a hill. Rider instability is a particular problem at slow speeds because steering corrections are bigger.