Why do you think Chunilal did what he did? Chunilal says he has no money; what is it that he does have?
Chunilal expected a friend to help a friend in need. He expected Bepin Babu to manage a job in his bad time. But Bepin Babu behaved rudely with him and forced chunilal to go for a revenge.
Chunilal did not have money, but he had great power of imagination. He applied his imaginative power to plot a psychological game playing against Bepin Babu to punish him for the same.