Weird Gmail login

So something really odd just happened on my phone and I cannot figure out any kind of logical explanation for it.

I went to make a new Gmail account, so I opened up an incognito tab on my Chrome browser (because I'm logged in everywhere else on my regular Gmail account) and when I clicked into the email address bar, it prompted me an email address that I didn't recognise. Even stranger than this, it also had a saved password …

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