The parent means, logging out
and staying logged out of the browser, would have exactly the same behaviour as logging out of your Google Account would in Firefox.
The whole point of the feature was just that:
1. “are you logged into your Google Account from the perspective of Gmail et al” is now the thing the browser chrome itself reports; and
2. you now need to be logged into your Google Account in the cookies sense for Chrome sync to function; logging out of your Google Account turns off Chrome sync.
Before, people could be in a state where they have Chrome sync enabled with foo@gmail, but are not logged into foo@gmail from a cookies perspective, and are potentially even logged into bar@gmail.
This is the state that has been eliminated—now, the browser chrome’s login state reflects your Google Account web-cookie login state, because they’re one-and-the-same; and every method that logs you out of your Google account from a web-cookie perspective, also logs you out of Chrome (and vice-versa.)
Consider the privacy implications of someone who logs out of Gmail, but is still logged into Chrome sync as said Gmail user; and then lets someone else use the computer. That is what is no longer possible.
It’s a privacy improvement targeted at the people who expect “logging out” of their Google account to be one unilateral action that frees a computer of all artifacts related to their original logging-in. Which, until recently, wasn’t true: if you originally logged in by entering your credentials into the “new Chrome profile wizard” (where they set up the credential as both your synnc and web-cookie credential), and then logged out of one, it wouldn’t affect the other.