Zoe ran vs Zoe was running

Yesterday my cousin, who is in 10th grade, asked me if could help her to write a book review. I don’t know why but the first sentence of the story in her textbook seems off to me from a grammatical point of view. Since I’m not a “native English speaker” I wanted to ask if this is correct or not.

The story begins with:

Zoe ran. Harder than she had ever run in her life. She ran through deserted streets, past derelict buildings. Somewhere, not far behind, she could hear the gang coming after her. [...]

Why does it say “Zoe ran”? Doesn’t it imply that she started to run? I’m sure the author was trying to say that she was doing it in a specific moment in the past (ongoing action in the past) so it should be “Zoe was running.” right? Or is it a matter of point of view? Thank you for your help!

Both are technically fine in most situations. However, especially in a book, where the style of the prose is as, or more, important that being perfectly correct, "zoe ran" may be preferable. It is shorter and, I can't explain why but suspect more readers would agree, is more emotionally evoking. Also, "was running" is more correctly used when you are specifying an exact time, or that something else occurred while she was running. It is unnecessary otherwise.

Each one has a slightly different meaning. “Zoe ran” implies we start the story with Zoe being still (or at most walking, but not running), but as soon as she heard the gang, that triggered her to run.

“Zoe was running” implies that the narrator started the story with the running scene. Telling you that the first thing we know is that she is running from something, and then explaining the reason why. This type of narration is called "In medias res".