Actually, I'm pretty sure that's what they're looking at. How much time people spend with modern apps vs traditional ones. How much time people spend in the start screen. The number of clicks. How the start screen is Invoked. What tiles are pinned. What tiles are unpinned. How often those change.
You know, actual usage data.
...and you seriously expect meaningful (if it ever can be) telemetry data to come out of a gimped dev preview?