In reply to Bud Kraus.

No, this article is about Gutenberg 5.1. WordPress 5.1 includes Gutenberg 4.8, since that was the latest version when the 5.1 beta started. The Gutenberg plugin features newer versions of Gutenberg features than WordPress core.

On a related note, I think the current plan is for WordPress 5.2 to include Gutenberg 5.2, since the planned release date of Gutenberg 5.2 is close to the planned feature freeze date of WordPress 5.2.

Yeah, it's a bit confusing, but eventually the Gutenberg version numbers will diverge from the WordPress version numbers enough to be less confusing, since the Gutenberg plugin gets feature updates more frequently than WordPress core.