Hi Martin,
Welcome to the Cryptomator Community 
You bought your lifetime license as an in-app purchase within the Cryptomator freemium app. The app was installed from the Play Store, receives its updates from there, and the in-app purchase is linked to your Google account. There is therefore nothing to worry about.
Family Library is the one thing that works differently: Google only allows paid apps to be shared with family members, not in-app purchases. See Google Play Family Library:
If you want to share Cryptomator with your family, the paid app Cryptomator: Full Version is the right product because it supports Family Library. Also you could use the license key variant of Cryptomator.
In one of this cases, send us a short message via support@cryptomator.org with your Google Play order number (it starts with “GPA.”) and we can refund the in-app purchase so you can buy the other app variant instead.