When a page is normally index and then later set to noindex it won't be automatically removed from the OpenSearch index.
Related code is this: https://source.int.netcentric.biz/git/projects/AICOM/repos/cn-website-search/browse/import/ingest/ingest.js#29-40.
Furthermore the check for noindex was moved to the query index, noindex-pages are not included anymore and need not to be checked in the ingest.js anymore.