Launcher on android is just that - an app to launch other apps. Other apps can and do run in the background, without ever being explicitly launched. Think play services, location provider, wifi connection manager, etc. Since google runs its stuff at the highest level - nothing can hide from it. Other apps, like netflix, utilise internal telemetry. Assholes like facebook push the boundaries to the limit and collect literally every input of every sensor to have as much data about your environment as possible.