This sort of announcement just emphasizes the extent to which Google observes ALL your web browsing behavior, thanks primarily to their eyes inside Chrome browser.
You know those warnings when you install a browser extension, about all the things that extension will be able to see and do? Well so can Chrome itself…
Crawlers do not use the browser back button or browser history. So the only way Google could observe such problems is by observing live human browsing behavior.
Also, we know from exhibits in the U.S. DOJ trial that Google does use Chrome browsing behavior as a signal in search ranking. It’s not a hypothetical.
Couldn't you instrument the crawler's browser engine to observe whether (while crawling) the page does any behaviors that would result in back button hijacking? No back buttons have to be clicked.
You just have to watch whether the mousetrap is set. Since you know how mousetraps work, you don't have to grab the cheese.