Dr. Reynolds' nonchalant greeting to Boo made Scout realize that someone actually had been making contact with the mysterious Radley over the years.
Of course... even Boo Radley got sick sometimes, I thought. But on the other hand, I wasn't sure.
Dr. Reynolds' "breezy" manner made Scout feel more at ease, and her embarrassment over calling Arthur by his ghostly nickname soon went away.
Scout was unusually outgoing with Boo, choosing on her own to sit next to him on the porch. Aunt Alexandra's constant demands for Scout to start acting more ladylike seems to have had an effect, since Scout led him into Jem's bedroom and then took his hand to escort him home. Perhaps Scout was remembering how Aunt Alexandra behaved after Atticus broke the news about Tom Robinson's death. "After all, if Aunty could be a lady at a time like this, so could I."