That Another John Doe never, ever had access to johndoe@gmail.com, they just gave a wrong address. That's not gmail's fault.
This. My wife and I have two flavors of this.
Her address is firstmlast@gmail.com. There people frequently forget the m initial and somebody else owns firstlast@gmail.com She's since started using dots first.m.last to mitigate the error.
My address is firstlast@gmail, where first and last are not globally common, but are fairly common in Scotland. Once a year or so, I receive email for somebody else that shares my name. I don' know his real email, but I've been "invited" on his family vacations 3-4 times now. Infrequent enough that I just respond "thanks for the invite, but I think you'll be disappointed when I arrive and not the Alistair you were expecting."
It's actually not a super common first and last, so firstlast@ knows when to who to forward.
I signed up for my university's email forwarding for alumni early on and got my first name as my email. For quite a while, I would get emails, including fairly sensitive ones, sent to me by not yet very email savvy people just assuming you could send an email to someone's first name and it would get to them.
I received 2-3 personal emails, but most of them are automated invoices.