So.. the gentil thought that the christian was far away because the sound of the ring was quiet (since it was in the pile of wool/fleece/whatever that is) and then he left the cave to check the pile of sheep-fur (which is outside?), he shook it and then ran away? What an odd fellow...
well.... yes. That is the meaning of the sentences, more or less. Grammatically it's very clear, so no confusion there. But the logics of the story... I also don't get it very well, to be honest. To me, it sounds like my grandmother telling me a tale that she knows very well, and forgetting some part of the story, so that it still makes sense in her head, but an external listener will just frown... "wait, what was that?"
Actually, the way I know the story of Tantalo, the idea is that the prisoner would hide below the wood, making the giant (gentil in this version) think the ring was outside. When the giant opens the door, the prisoner would get away running like hell. But the giant would hear the "hemen nago" yelling and run after the escaping prisoner. He (the prisoner) would eventually cut his own finger with the ring and throw it down a cliff or into a river, and the giant would go after the ring, getting drowned... so that's the logic series of events. The sentence " Orduan, jentilak larru pila astindu eta lasterrari emanda jesus batean handik alde egin omen zuen" breaks everything down... why the hell would the gentil shake the pile of wool if he thought the christian was far away?? I think the narrator just made a mistake.
... by the way, the story as I know it should have the element of the captor being blind (that's why the ring was necessary for him to check that the prisoner was still there, and that's how he can get tricked into throwing himself down a cliff!). In some versions, the prisoner has blinded the captor after being taken, in others he was just blind beforehand. I have the impression that the narrator is mixing the story with the (similar) one of Polyphemius, were the prisoner would get under a piece of wool/fleece to make the captor believe he was a sheep. The blinded captor was supposed to be on the entry of the cave/house, blocking it and controlling that only his sheep could get past the gate by passing his hand on the back of the animals. The prisoner, disguised as a sheep, can thus scape.