Based on the wording, it sounds like it's autocomplete data — "I suggested this for what they typed or handwrote, but they chose this instead."

If so, it probably wouldn't include passwords (since password fields intentionally disable this kind of feature), and it shouldn't include the full contents of emails, just telemetry on how they were typed.

But Microsoft really ought to have explanations so we don't have to guess, and they ought to know that. I'm assuming this is on their itinerary and the documentation department is just lagging.