That quote is why a lot of people assume he was balefired - because the Dark One couldn't bring him back because of 'how he died'. But also 'where he died'. The only thing I can come up with to fit that is that he was killed by a small amount of balefire, such that if he were killed closer to Shayol Ghul, the Dark One might have been able to bring him back. Because RJ did say that proximity to Shayol Ghul helps the Dark One catch the soul, and he also said that a very small amount of balefire would not prevent transmigration.