Ask HN: What's Going on with Gmail and YouTube?

I recently received an email in my gmail inbox addressed to a completely different recipient (my email address is nowhere in the raw contents), containing a YouTube terms of service update from 2019. I found a reddit post with a few more people in the same situation that goes into more detail, including strange sender routing and possibly invalid dkim/etc being presented as valid by gmail: https://www.reddit.com/r/Scams/comments/mokin6/phishing_email_pretending_to_be_from_google/

What could this be? An exploit of Gmail, a bug sending people the wrong mail? Concerning in any case.