That's in fact also very technically feasible. They're already running small classifier models on both your inputs and your outputs. These models are said to be in place for safety, but they could answer 2 questions: (1) is this a safe query, and (2) is this query about X, Y, or Z topics (which happen to be high alpha / very interesting to Anthropic).

If #2 returns a yes, the input/output are temporarily stored (say, for 30 days) while a background process cleans up PII and generalizes the prompt to be "clean", then the clean prompt that is not yours anymore is stored aside and used for training, product development, etc.