When we eat food, we need to chew the food properly so that it is broken down into smaller particles. These smaller food particles then pass through the oesophagus to reach the stomach. Since Boojho was eating in a hurry, he did not chew his food properly. Moreover, while he was swallowing his food, the large food particles might have entered his windpipe causing him to choke. This is why Boojho was coughing while eating.