The proposed patch is intended to included as a whole. One part will not work without the other. The problem with the current behaviour is that since
WICKET-4021, the page provider retrieves a page from the page store in isNewPageInstance. This instance is then touched by the AbstractPageManager, however the PageProvider does not keep hold of it. Next, in getPageInstance, a new instance of the same page is fetched from the page store. This instance is not touched, because another instance of the same page is already touched. This second instance is used in the request, but at the end of the request, the first instance is stored in the page map.
As you can see, the proposed patch is an improvement to PageProvider (removing responsibility from that class that shouldn't have been there), a performance optimisation (do not fetch the same page from the page store multiple times) and a bug fix (the page used in the request is now stored in the page store, rather than a stale instance).