How does the author present the theme of alienation in the story, The Japanese Quince?

Mr. Nilson is alienated from both nature and humankind. Although he praises himself for taking a walk in the square on a beautiful morning, he takes his newspaper with him. Still, the strange sensation does not abate, and he suspects it might be caused by something he ate. Upon encountering the quince tree, his first instinct is to find out exactly what species it is, rather than simply enjoy the flowers. Towards the end of the story, when the blackbird resumes its singing, "that queer sensation, that choky feeling in his throat" returns, further underscoring his alienation from nature.