I think you're right about the right side being the folder name. No I wasn't in the ST3 app contents, but that reminds me of what this folder was: the base path to app contents to a different app.
I noticed it when I created a new file after re-opening ST3, so I've gone off and tried to replicate the behavior but can't. And somehow over night, the weeks-long quirk is gone.
I'll keep an eye out for this, and if I can ever recreate it, I'll post the steps.
Thanks for your response!