Yeah, that’s what I expected to happen.
Basically*, Google says to the new Sotonians.com…
“Hi new Sotonians. that twat Cobber has asked me to vouch for him. I can confirm that he is a twat and his email address is email@example.com”
and then the new Sotonians says…
“Oh, hi Google. Lol. How things? BTW thanks for authenticating that twat Cobber. It turns out I’ve got an account for him for that email address firstname.lastname@example.org - something about being a technofuktard. I’ll log him in with that username. Lol.”
and then Google says
“Lol. What a twat. Yeah, all good here hope you’re well. Saw your missus on Google Photos the other day. Nice arse. Chat soon. G.”
*Bletch dumbs down OAuth2 for a complete Techofuktard.