It's the 'He won't hurt you ...' syndrome.
All dog owners say that, as their rampant beast leaps up at you trying to knock you over.
What they should really say is "He has never hurt anyone to date, but he is an animal, and like all animals, he has the potential to attack without warning ..."
But pet owners, and it seems wild animal breeders, lapse into a false sense of security, and that is what seemed to happen here.
With dogs, it's often a small child who pays the price for owners' rank stupidity in not understanding that their pet is an animal, and will behave as animals do - unpredictably.
In this case, it was the breeder, and ultimately the lion.