Theory:

     It was a rough day. A strong wind blew against the high, plate-glass windows. Smoke filmed the wintry city and the air was grey with a thick frost. Having completed his usual tasks, Mr Purcell again mounted the high stool, and unfolded his morning paper. He adjusted his glasses, and glanced at the day’s headlines. Chirping and squeaking and mewing vibrated all around him; yet Mr Purcell heard it no more than he would have heard the monotonous ticking of a familiar clock.

     There was a bell over the door that jingled whenever a customer entered. This morning, however, for the first time Mr Purcell could recall, it failed to ring. Simply he glanced up, and there was the stranger, standing just inside the door, as if he had materialised out of thin air.
Explanation:
 
After narrating about the daily routine of Mr Purcell, the narrator stated the weather condition of the city. It was a hard day. A strong wind buffeted the lofty, plate-glass windows. The town was engulfed in smoke, and the air was bleak and frosty because it was winter season. After completing his daily task, such as opening the shop, Mr Purcell again mounted on the high stool and took his newspaper. Then he spread out the morning newspaper, adjusted his spectacles, and gave a quick look at the headlines of the day.

While he was reading the newspaper, a lot of noises were vibrating around him. Mr Purcell was surrounded by chirping, squeaking, and mewing, but he didn't hear it any more than he would have listened to the monotonous ticking of a familiar clock. The chirping of birds, the squeaking of rats, and the mewing of cats could all be heard throughout the pet shop, but he was blissfully unaware of it. It implied he was used to those sounds, and he was never bothered by that, and it wouldn't disturb him.

The narrator later added that there was a bell over the door that jingled whenever a customer entered Mr Purcell's shop. So, while he was reading the newspaper, the jingling sounds of the bell would alert him that the customer had arrived.
 
bell-37464_1280.png
Jingling bell

But on that fine morning, Mr Purcell would recall that the bell failed to ring. It implies that he spotted someone entering his shop for the first time without hearing the bell jingle. When he looked up, he saw a stranger standing inside the door, as if he had materialised out of thin air. The phrase "out of thin air" in this context suggested that someone or something appeared unexpectedly without any intimation. The sentence implies that usually, when a customer opens the door to enter the store, the bell over the door would ring. But that day, when the strange man entered the shop unexpectedly, the door bell did not jingle.
 
Meanings of the difficult words:
 
S.No
Words
Meanings
1
Out of thin airSomeone or something appears in a sudden and unexpected way
2
FrostCover something with or as if with small ice crystals; freeze
3
Glance Take a brief or hurried look
4
HeadlineA heading at the top of an article or page in a newspaper or magazine
5
Chirping Typically of a small bird or an insect utter a short, sharp, high-pitched sound
6
Mewing High-pitched cries characteristic of a cat or some kinds of bird
Reference:
National Council of Educational Research and Training (2007). Supplementary. I Want Something in a Cage - L E Greeve (36-42). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.