One person can be the audience for an authors work

This is correct statement, one person can be the audience for an author’s work.

This can be explained in two ways.

One is that in writing fields people sometimes and in some area of writing do not want to read anything written for everyone, they want something specific for that single person and that individuality is the beauty of that writing.

Another way to explain this is that sometimes someone write keeping a specific person or personality in mind and writes for him/her, if only that one person appreciates the work, the author feels successful and contented.