@twinklecake A few ways, first are mannerisms, his was identical to Lento. He's unique in the way he treats others and is more of a teacher than an adventure, when looking closely at how he guided them, it was obvious that it was not his first time, even though it should be. Lento's body was also never found, nor was there any report of his death, thus his body seemed to have just vanished.
While she wasn't certain, she had a gut feeling that something happened to him that caused him to hide his identity.