The first Chrome did use a fork of WebCore, the HTML part of WebKit, as its rendering engine, but added its own V8 JavaScript engine. The speed of JavaScript was the main differentiator. And _that_ was very different from Safari, and every other existing browser ... The quote is correct.

V8 kept getting even faster, including adding faster RegExps, which pushed the other browsers to speed up their JS too. Firefox is now using that RegExp implementation too, even if they're not using V8.

WebKit was itself a fork of the KHTML browser engine. And just like WebKit diverged from KHTML, Chrome diverged from WebKit.