Hey OP - I made Blankslate.io as a side project a little over a year ago. I can't tell whether you've found a vulnerability that's letting you see private notes, and if you have please tell me here or via email (tomasienrbc @ gmail).

However, Blank Slates can be public or private at the user's discretion, so if you've just run a script looking for public notes, then that's just fine. I would love to know either way, so hope to hear from you more!