My sign in as google uses the @gmail address, which I don't have access to other than signing into google, so I wouldn't be able to get the reset email link.
Interestingly, since I use my own domains, my facebook signin is different than my gmail address. But interesting, I've never tried using a second oauth as a match to the first.
I know this is how discourse handles federated identity: it uses the Oauth2 server to match the account's email address against the Facebook/Google/Twitter account's stored email address. Spotify works this way too.
