There were many things to consider when considering the whole incident, like how Lucien's golden dragon flames could burn away the corruption of the void. No, maybe it wasn't the pure golden flame; something of a special spell or technique was mixed into it as well. Lucien probably learned it from the same person who taught him the external sense.
But there was one thing, one biggest thing which he had to acknowledge no matter what, which is that Lucien indeed risked his very life to rescue him, yes he had a tool that could fight off against the void, he was probably pretty confident considering his character that he would be able to save himself from whatever predicament he was in, that was likely Lucien's thought process before he jumped in. But the situation turned out far worse than he expected.
