When pipelines with retries on `retry:when` `api_failure` condition are rerun?

Question

What api failures are caught by retry:when api_failure in below pipeline?

test:
  script: some api call
  retry:
    max: 2
    when: api_failure    

Does gitlab detect any api call failure inside the -script by analyzing network traffic, for instance or api_failure catches GitLab api failures only?

Couldn't understand that from the docs