Let’s say that my YouTube name is BoboJones, and that’s the only place I have ever used that name. I just received an email with a subject line that said, “BoboJones sent you a video,” (as sometimes happens when you send a link from a site to someone through that site) and with the link embedded in the body of the email. I have only moderate interest in the subject of the video, but I did not send anyone that video, including myself. And is it possible that YouTube sent that video not only to me but to people on my email list? What happened? Is this another case of Google making use of data for marketing purposes? This is spooky to me.
Sender addresses are easily spoofed. Some hacker out there got a list of email addresses somehow associated with your YouTube handle and sent out a blast of mail. It could be from your account being compromised, it could be from someone else’s account being compromised, it could be from vulnerabilities in the system since your email addresses aren’t always hidden.
I would guess it’s very unlikely to be spam from YouTube itself.