Gmail accepts multiple forms of email addresses for a single account. email@example.com is identical to firstname.lastname@example.org. I often get subscribed to email lists I don't want using a variant of Gmail address that I never use. Also, plenty of people using forwarding addresses; it may not be clear which address was the target.
Either you or your friend is misspelling their address (more common than you might think, I get opt-in mailing-list mail for email@example.com, intended for firstname.lastname@example.org), or you've encountered a bug.
Google's own email@example.com mailing list has this as the "To:" field:
And at the bottom of the message:
To unsubscribe from this group, send an empty message.
I had to ctrl-u and check the "Delivered-To:" and "X-Forwarded-For:" headers before I could unsubscribe.
(I'd tried to unsubscribe previously but the subscribed email account forwards to my main account so replying with an empty message didn't work. This thread prompted me to dig a little deeper and finally get one less piece of email per day - thanks HN!)
Or English isn't their first language. That was my impression. Granted, I bailed partly because of the grammar, too but that was after realizing it was a mixed list of soft skills, not algorithms or tools or whatever. Once it wasn't what I expected, the writing didn't help keep me.