Searching in Google and visiting links which open in the app doesn't mark those links as visited when you return back from app to search results in browser.
This is probably in the hands of the browser and out of the hands of the SE team.
The browser has not accessed that page before. It is not in the browser's history. Therefore, as far as the browser cares, that link has not been visited by it.
You sure did click on it, but the browser didn't handle it and as far as it's aware you've never been to that page in your life.