BigQuery IO Source is not Exporting to GCS as written in documentation

Did some check on the beam code and find out that DataFlow is querying BigQuery and retrieve the result using pagination [1]. As per our understanding, this means no parallelism on reading BigQuery table. It is contradictory to what the documentation is telling us [2].
 
Is this some kind of work in progress? I'm filing as a bug since documentation telling me that it is using GCS meanwhile it's using NativeSourceReader which yield data per row as iterator.
 
[1] [https://github.com/apache/beam/blob/520b3a24e49306c30940ceab09100d775a04d28e/sdks/python/apache_beam/io/gcp/bigquery.py#L1083](https://github.com/apache/beam/blob/520b3a24e49306c30940ceab09100d775a04d28e/sdks/python/apache_beam/io/gcp/bigquery.py#L1083)
[2] [https://github.com/apache/beam/blob/520b3a24e49306c30940ceab09100d775a04d28e/sdks/python/apache_beam/io/gcp/bigquery.py#L60](https://github.com/apache/beam/blob/520b3a24e49306c30940ceab09100d775a04d28e/sdks/python/apache_beam/io/gcp/bigquery.py#L60)

Imported from Jira [BEAM-5352](https://issues.apache.org/jira/browse/BEAM-5352). Original Jira may contain additional context.
Reported by: rendybjunior.

Start with sdks/python/apache_beam/io/gcp/bigquery.py at the NativeSourceReader reference near lines 60 and 1083, and compare the documented GCS behavior with the pagination behavior described in the issue. Determine whether the implementation or documentation is incorrect; done means the discrepancy is resolved and the documentation accurately describes the source behavior.

Written by the indexing model from the issue text.