I would assume the telemetry would include what build/branch you are playing. Since the internal test builds are known and different from the public builds they can filter out the QA team and anyone in a closed testing group like they are trying right now with pre-experimental.Also, what are the data worth if there are many players who spend most of their time in game testing (and restarting the world often) rather than playing?
Knowing what % of players are on what stable or experimental build is also valuable data for TFP.