I just digged through the source code and found it in the package Keyguard.
I’m currently not sure if we can pull these features out of that package and put them into the clock widget. The F-Droid description is wrong 
Edit: So Keyguard actually is the part of the lock screen that handles the unlock mechanism (e.g. slide to unlock, pin code, password or pattern). Seems like Fairphone built the peace of mind widget right into that.
Edit 2: Ok, I’m confident that we can enhance the clock widget with the Peace Of Mind and eventually the remaining battery life functionality. However it is currently unclear to me if the “Your Fairphone since” functionality works on other devices as well. If not, we could simply only display that on Fairphones. The data for that is read from /persist/board_date.bin. The second thing is that I don’t know how Android handles lock screen widgets and whether it is actually possible to install this as lock screen widget on a stock ROM.
Edit 3: There needs to be some work done, especially regarding the battery statistics (widget is using classes that are not availabe to normal apps). Will take a few days.