Leonardo Driver on Windows > strage behavior

Hi,

I hope to use the right forum.

Weeks ago I connected a Leonardo on Windows without installing a driver and it worked!
I damaged the Leonardo and had to buy a new one.
When I now connect to windows, windows needs to install a driver?

Could anybody please explain this strange behavior?

Why is there on the one hand no driver needed; ont the other hand it is?
Thanks
Regards, Mario