Is my taking the initiative to justify the reason for ending a conversation with a young man—out of fear of developing feelings towards him that are displeasing to Allah—a sin that warrants Allah's wrath?

You did well by ending the conversation with this young man, because such conversations are a gateway to evil and an entry point for Satan to tempt the children of Adam. Many incidents bear witness to this, as Allah the Almighty said: "O you who have believed, do not follow the footsteps of Satan. And whoever follows the footsteps of Satan - indeed, he enjoins immorality and wrongdoing." And happy is he whom Allah protects from Satan. There is no blame upon you, Allah willing, for what you did by returning the call to this young man, as you clarified the reason for ending the previous calls, and that it is something that does not please Allah the Almighty. We advise you to be cautious in the future regarding any private calls with young men, as they are a cause of temptation.