Theory:

     You’re sure that I did go to Ranchi?”
 
     Chuni’s look of amazement was not unmixed with worry.
 
     “D’ you mean you have doubts about having gone at all?”
 
     “Did I go? Do you remember clearly?”
 
     Chuni sat down on the sofa, fixed Bepin Babu with a long, hard stare and said, “Bepin, have you taken to drugs or something? As far as I know, you had a clean record where such things were concerned. I know that old friendships don’t mean much to you, but at least you had a good memory. You can’t really mean that you’ve forgotten about the Ranchi trip?”
Explanation:
 
Chunilal was sure that Bepin had gone to Ranchi, but he couldn't remember the exact year of it. When Chunilal couldn't decide whether to go with \(1958\) or \(1959\), Bepin understood one thing. According to Chunilal, Bepin would have gone on a Ranchi trip somewhere between 1958 and 1959, although he wasn't sure about the year. That was when the point became crystal plain. However, Bepin wanted to reassure it, so he questioned Chuni, "Are you sure I went to Ranchi?"

Chunilal had not expected such a question from Bepin because, earlier, Chuni had assumed that Bepin had trouble recalling his Ranchi trip's exact year. However, later, when Bepin asked him further about the trip, Chunilal understood that Bepin forgot about the entire trip.
 
Chunilal was surprised to know that his friend had forgotten about an incident that occurred only some years before. He even asked him the question, "Bepin, have you taken to drugs or something?" for he knew very well that Bepin has a good memory.
 
Chunilal was taken aback and sat on a sofa for a while, occupying Bepin's home. For a long time, he focused his gaze on Bepin. He then began to converse with Bepin in a mocking tone. He mentioned that Bepin has a good memory, even if the past connections aren't meaningful to him.
 
Chunilal's statements were so sarcastic, which referred to Bepin's unfeeling attitude toward their friendship. Despite the fact that Chuni's remarks were sarcastic, he commended Bepin on his strong memory power. So, Chuni couldn't accept the fact that Bepin had forgotten about his trip.
Reference:
National Council of Educational Research and Training (2008). Honeydew. Bepin Choudhury’s Lapse of Memory- Satyajit Ray (pp. 59-69). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.