While true it seems like the rings are adjustable in terms of attaching to the blade hilt so you can make the rings tighter or looser. it needs to be adustable to get around the ring on the hilt to attach it. so even if rudy didnt know the exact dimensions of the hilt she could make it so it attaches reasonably strongly.
A sword is quite heavy, approx. weight in the kg, and the ring’s contact point is in the cm. The friction of that contact point has to sustain all that momentum from the spinning and drawing of the sword.
And, even if it is fine in the initial demonstration, the grip of the sword will have dirt, sweat, and whatever else, which will reduce the friction of the ring. Further, if the grip is made of or layered with fabric, leather, bark, or anything soft, it will be fine now, but eventually it will give way to the ring.
Tl;dr “attaches reasonably strongly” IMO is insufficient.