I believe I do have a timeline of events that you might find illuminating.
Vanessa approaches him and asks that he tell her a story. Uncle Newt replies that he does not know any stories. Vanessa is incredulous, believing that all uncles should know stories. Uncle Newt reminds her that he is not truly an uncle, but just poses as one to get free pipe racks at Christmas.
Instead, Vanessa tells Newt the story of Cinderella. He repeatedly interrupts to question elements of the story, such as the priorities of the Fairy Godmother and the practicality of glass slippers.
When Vanessa has finished, she repeats her insistence that Uncle Newt should learn some stories. He agrees to attend to the matter.