Which side of the story do you think is true?

I believe Olaf's account is the more likely one considering the ancient bard texts claiming he was a fraud claim that Numinex was dying of old age and thus weak. We know this can't be true as they are immortal and even the oldest of Dragons ie Alduin and Paarthurnax are still strong enough to claim leadership over Dragons.

you make a good point about how dragons are immortal...

I think the writers might have messed this one up