Ask HN: How does tripadvisor know all my Google accounts?

I clicked a google search result that brought me to tripadvisor and in the top right of the page there was a popup titled "sign in to tripadvisor.com with google" listing all my google accounts (name, email and avatar).

this was not a google iframe, it some just some html inside tripadvisor.com page (I can see my info when I click view source). I never signed up on tripadvisor with any google account, especially not with my work google account (which was also in the list). so how does tripadvisor know all this? after clicking the X on this popup I can no longer reproduce it.