The authorial intrusions in this story are relatively subtle. Hemingway does not, for example, address the reader directly, but rather, he simply "pulls back" his focus a little bit, telling us things that are more hypothetical or omniscient than he had other places.
A good example of this is the following:
The waiter watched him go down the street, a very old man walking unsteadily but with dignity.
The observation "but with dignity" is more of an intrusion than the strictly limited observations Hemingway had allowed himself other places.
These places mostly color the story, guiding our emotional interpretations a bit. Some shape our understanding of the characters.
"No, it is not," agreed the waiter with a wife. He did not wish to be unjust. He was only in a hurry."
"Finished," he said, speaking with that omission of syntax stupid people employ when talking to drunken people or foreigners.