I’m fairly certain they are. My links ended up indexed in Bing search results. The only place they were ever rendered was in private emails to users. Bing should not be indexing that.
For a bit of added "fun", Google will do the same, but if you add a page to robots.txt and set noindex then they won't process the noindex parameter and external indexing sources might still generates search results: https://developers.google.com/search/docs/advanced/crawling/...