The nature of the angel in the story is ambiguous. By referring to the angel as "an imaginary dot," the author could be suggesting that the angel was a figment of the imagination. However, the author could also mean that Elisenda keeps watching the angel flapping away until she can no longer see him, not even the faintest trace of him, but she imagines that she does.
The story is written in the style of magical realism. This literary style combines realistic and surreal elements. The angel is presented in a kind of matter-of-fact, even mundane way in the course of the story. In fact, he has ragged wings that are missing half of their feathers, and he seems far from being an angel of myth. He instead resembles a broken-down old man. However, when he takes flight, the reader, and Elisenda, have to wonder whether he really is an angel. The story asks the reader to remain mystified by this creature and to remain wondering whether he is real or a figment of the imagination.