I see nothing online about anyone else reporting this issue. Since you aren't sharing notes, you should also think about whether someone has shared a note with you at some point. A shared note has a little icon of a a person's shoulders & head in a circle to theft of the note...
If this problematic note doesn't show the icon, it's probably not that.
Do you perhaps share iCloud or another Apple device with someone else, who may be creating a note on your Mac or other iDevice that then lands in this one's notes app. For example, if I create a note on Mac, it "spontaneously" shows up on my iDevice and vice versa. If someone else had access to my other device and created a note, it would seem to be magically doing what you are describing.
Some people use notes like a scratch pad. If someone is using another Apple device on your own account, maybe they are sticking a new story in a note wanting to get to it later?
If you think perhaps there could be anything to this, you might try turning off iCloud Notes for a little while and see if it spontaneously creates one of these. That would rule out anyone else with known access and/or perhaps someone else with unknown access from using your AppleID iCloud or maybe an old device still linked to your account.
Else, I start guessing a unique bug or your iCloud account MIGHT be hacked (which a simple change of password could test that probably-wrong guess). If the former, someone else will need to chime in saying they have the problem too for it to be a potential Apple OS bug. As is right now, this appears to be unique to you.