If you were to go back to the same search result page and click on another result within a short timeframe they will assume you “bounced”.
They also have Google Analytics littering the majority of the web, so I’m assuming that gives them a signal as well.
Google links directly to search results now, they stopped using the tracking redirect years ago. They probably track clicks and scrolling directly on the SERP with JS.
Google Analytics is absolutely not used for ranking purposes. GA is far too unreliable and gameable to be used for anything like that. It's more likely that Chrome and Google Safe Browsing are used for tracking user hits.
I rather open a new tab from search results and close it instead of clicking the link and going back. I imagine many people do that.