That very brief segment of the article pretty much collapsed a decade of time into two sentences, but yes it appears to be denoting the transition from CentOS [Linux] to CentOS Stream.
In other words, how was downstream CentOS considered a beta or "a preview of what was coming down the pipe"?
That segment of the article in particular is very poorly written, and seems to aim for sensationalism rather than accuracy.
To answer your question directly: it wasn't.