Although Number Three didn't say anything when he mentioned that Klaus managed to save Hanna this time, Klaus didn't need anyone to remind him of similar situations, like when he witnessed Haniva's death.
He knew that he had failed to save her then, but now it seemed he had somehow managed to prevent Hanna's death.
Had he been a little weaker or, worse, slower to enter Ruin City, Hanna would have blown herself up by now, taking with her the 23 men who played a part in her Kahlani losing her purity in the most painful and humiliating way.
When he smiled at her in Ruin City, Klaus severed that line of fate, which seemed to lead only to her death.
Now, he discovered that she was someone dear to him, someone he needed to understand in order to figure out what had led him to enter reincarnation in the first place. One could say that Hanna was one of the keys he had been searching for over many lifetimes.
