What does Holden tell the woman on the bus, and why?

In chapter 8, Holden leaves Pencey Prep and an older woman named Mrs. Morrow ends up sitting next to him on the train. When Mrs. Morrow notices Holden's Pencey Prep sticker on his luggage, she asks if he knows her son, Ernest Morrow. Holden responds by telling the woman that he is familiar with Ernest and introducing himself as Rudolf Schmidt. Holden then proceeds to lie to Mrs. Morrow by speaking highly about her son, who is actually someone he does not find interesting, charismatic, nor friendly. Holden goes on to tell Mrs. Morrow that Ernest "adapts himself very well to things" and is popular among his classmates. Holden even tells Mrs. Morrow that the students encouraged her son to run for class president. Holden gives the reader insight into why he enjoys lying to Mrs. Morrow by saying,

Old Mrs. Morrow didn't say anything, but boy, you should've seen her. I had her glued to her seat. You take somebody's mother, all they want to hear about is what a hotshot their son is.

Holden then tells Mrs. Morrow that Ernest was too humble and shy to run for president, which causes her to smile. After asking Mrs. Morrow to join him for a cocktail, she asks Holden why he is heading home early, and Holden responds by telling her,

I have to have this operation... It isn't very serious. I have this tiny little tumor on the brain.

Holden's entire conversation with Mrs. Morrow further characterizes him as an unreliable narrator, who has an affinity for lying. The fact that Holden's lies are not harmful is significant and suggests that he is a relatively innocent, naive teenager. Holden's claims are also ludicrous and unfounded, which also emphasizes his immaturity. Essentially, Holden amuses himself by telling numerous lies to Mrs. Morrow on his ride back to New York. Holden's brief interaction allows him an opportunity to escape his loneliness as he humors himself on the ride home.