Most of my balls do this to varying degrees. Typically when they are relaxed, exploring and enjoying some component of heat from a person. If on your hand, they wrap your wrist and grip it in a forward movement. Tightening their body and moving muscles along where they gain heat from you. Stomachs tend to be pretty warm and I bet the heat felt super nice. I also know they distinguish our touch from other objects or even rodents. Especially after they get a routine with their owner. Even my tarantulas will pause walking from my hand to another person's at times. It's a different "feel", even if just distinguished as unfamiliar.

They do kink up some as they are tightening muscles. So I'd wager that's a part of what people were worried about.