https://chromium-review.googlesource.com/c/chromium/src/+/4156731
Looks like it’s based on Private State Tokens which are Google’s implementation of Privacy Pass. It’s basically just a privacy-preserving way to bypass CAPTCHAs. Apple has a similar thing with their Private Access Tokens. The info they’re talking about is likely just the Private State Tokens themselves which are essentially just letting you bypass the CAPTCHAs after you complete one successfully. They’re stored in their own separate area away from other browser data.