The data is less about what you are personally doing and more things like which device does a user have, which country is a user from, how often do they use the app, and how often do they click on ads.
You can dig more into what admob means by usage data here: https://support.google.com/admob/answer/9263723
We do know what defines active. An active user on Lemmy is someone who has made a post or comment within the last month.