An honest person who doesn’t want attention of any sort, Bella just wants to know what happened so she can feel secure and stop questioning her sanity. When Edward overtly questions her sanity here, he’s trying to make her doubt herself—which, in turn, makes Bella feel even more off balance. But Edward’s response also begs the question of why he’s so interested in convincing Bella she saw something other than what she did. He seems to have something to hide.