Feng Xue looked, well… she looked like she was electrocuted. Sort of anyway. And Yang Jingshen wisely acted as if he couldn't see this. With time, he had realized one very important thing— that pretending too much in front of this person was not advantageous to him in the long run.
Let's consider the fact that this cousin sister of his knew the original Feng Xi well, and could easily spot even minor differences. So, what? He was supposed to have amnesia, right?
It was the memories of a human– more like memories of someone's past experiences were what actually made them the person they are today. So without his– or rather without Feng Xi's memories, what kind of similar personality could he possibly possess? It was the case of having a totally clean slate ah!