It is always up to the dog owner to control their dogs. Train your dog to have a good recall, and keep them on lead or trained to walk at heel with distractions, and you should never have a worry about jumping into a hot spring, or running in front of a car. If your dog can get out of a collar, use a gentle leader or halti-harness, both of which stop pulling.
If anything, the owner should be in trouble, not a leash company. I saw nothing about a defective leash, but if you buy a quality leash appropriate to your size dog it should last you a lifetime.
Sad story. I commend the man's bravery if not his judgement.