Didn’t wanted to be the nitpicker ^^, so sorry when my detailed questing annoyed you 
I’m often just interested in “how it works” in detail.
And you are 100% right → the result is fair enough. It was just somehow surprising that it is possible with “normal” (non-root) privileges. 
The reply in the other thread
probably explains that the folder (in /system) is still exists after uninstall - it just keeps the apk.