مَنْ asks about a person, and ذَا adds a demonstrative sense. Together مَنْ ذَا؟ means “Who is this?” Replying merely أَنَا does not identify a visitor.
كَأَنَّهُ كَرِهَهَا uses كَأَنَّ for an impression: “as though he disliked it.” Jabir reports the Prophet’s ﷺ response rather than an extended conversation.
At a door or on a call, when someone asks who is present, a clear name or recognizable identification is more useful than an unexplained “me.”