Strange listens to Yuya. He still doesn't really know how Yuya knows all this. Perhaps he talked with Lambert? Or more likely, Yuya's just observant. He's certainly more observant than Strange is, he'll give the kid that much. So if Yuya thinks that Lambert is worried about himself and worried he can't change...then Strange will believe him.

And if Lambert really is worried that he's not anything more than just a killer or a witcher, then Strange feels even more terrible for putting him in that position in the first place.

"I never said I thought he was a monster," Strange clarifies, with a small frown. "He's abrasive and blunt, but certainly not a monster. He's one of my dearest friends. I certainly couldn't think of anyone that close to me as a monster."