dkl65:
I thought that it was the defense mechanism breaking the power connection, because I think that I heard a click. But the Arduino still had power to it. Does anyone know what haapened?
You did not active the poly fuse on the Arduino. Instead you activated your PC's supply protection. You saw readings on your Multimeter because the PC kept cycling power to the USB port to see if the short had been removed yet.
The Arduino's PolyFuse would not "click." That isn't how it works.