> ...wouldn't that still imply that Google are parsing Docs in some manner if they're able to be flagged for ToS violations in general?

Public documents in Google Docs are used as targets for spam or phishing campaigns pretty frequently. (The latter is usually by way of Google Forms, which can be used to drop content into a spreadsheet.) Google needs some way to allow this behavior to be flagged, and ideally to recognize it before it gets abused.

Private documents are another matter. Even there, though, I imagine they are obliged to scan some content, e.g. checking images against child pornography databases.