Electrical Short - What Just Happened?!

You say the battery voltage was ok.
That does not mean that the battery is functioning to specs.

You can not check the battery without putting a load on it. This can usually be done by putting the meter on the battery and then turn on the lights. Or turn the key while measuring the voltage.

If one or more cells in the battery has OPENED, no longer has an internal connection, a battery can and usually will show 12 VDC or normal voltage for the battery.

If one or more of the cells is shorted, it will read a lower voltage without a load.

I can explain it but it would take me awhile to set up the basics of an electrical circuits. Which I am really not willing to do at this point in time, so trust me or don't