iCloud Got unexpected "Reset Your AppleID Password" email

[macuser_123]

Hi,
Today I received an email from Apple with the subject "Reset your password or unlock your AppleID.", the body reads (edited):
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You recently requested to reset your password or unlock your Apple ID. Click the link below to continue.

Reset Password or Unlock Apple ID

If you didn’t make this change or if you believe an unauthorized person has accessed your account, go to iforgot.apple.com to reset your password immediately. Then sign into your Apple ID account page at https://appleid.apple.com to review and update your security settings.

Apple Support
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I did not request a password reset, so this must have been initiated by someone else. I checked the email headers, and it appears to be a authentic message from Apple rather than a spoofed email. I know these things are sometimes attempted by various hackers looking to get lucky and get into an account, and I assume this is an instance of this, but something is odd to me. The email address this message was sent to is one of my seldomly used, non-icloud.com addresses, that has never been registered as an iCloud username. So my question is, how would someone get Apple to send a password reset message to this email? I tried to replicate it by going to iforgot.apple.com, but when I enter this particular email address, it gives an error message "This Apple ID is not valid or not supported", and will not go any further. So how was this particular message sent?

 

[macuser_123]

Ok, followup to my own email. I did not realize that the AppleID and the registered email are two different things. So I did an AppleID lookup, entered the email address, and did come up with a valid AppleID. And when I entered this AppleID into iforgot.apple.com, I was able to generate the same reset password email that I got (unsolicited) this morning. But how strange, I am almost certain I never created this AppleID, but if someone else created it, wouldn't I have gotten an AppleID creation email notification? Maybe I did create it before and am just becoming senile; anyways, at least part of the mystery is solved, if only to raise other questions.