Does the browser still stores the website you visited?Private Browsing [incognito Firefox]

As they clearly state in their website they mention that

What does Private Browsing not save?

• Visited pages: No pages will be added to the list of sites in the History menu, the Library window's history list, or the Awesome Bar address list.


• Cached Web Content and Offline Web Content and User Data: No temporary Internet files (cached files) or files that websites save for offline use will be saved.

Considering this Scenario

If I open a tab in incognito Mode as per below screenshot.

After I close the tab It gives me an option to Undo Close Tab and If I click on it,This restores the tab which I closed.!

So Does this mean that this statement is untrue? Cached Web Content and Offline Web Content and User Data: No temporary Internet files (cached files) or files that websites save for offline use will be saved