Edit: Hey, downvoters, it's not possible to just use Google's login mechanism without prompting an initial OAuth flow at some point in time. If it is, instead of proving me wrong here, tell Google how and you can make some good money out of it.
As was said below, if you want, you can revoke tokens here: https://myaccount.google.com/permissions
What this seems like is after the user initially logged in and consented with Google, Quora went ahead and decided that they would initiate the oauth flow whenever the user visits the page regardless of whether the user explicitly hits the login button or not.
Very creepy
To break the link, go into Google and see what sites, apps, etc you granted access to. That's a good thing to do regularly anyway with every social provider.
I wrote about the implications of poorly implemented and abusive social authentication practices last month: https://www.scmagazine.com/home/security-news/using-social-a...