Selecting proper bypass diodes for solar panel
You didn't short circuit the solar panel, you connected one backwards against three others.
The current from those three solar panels was enough to have excessive current flow through the diode.
The diode conducted because it was wired backwards (along with the panel).
When diodes are overloaded they usually fail short circuit. If there is enough energy they overheat and the epoxy splits.
Even though the diode is rated at 8A, they are also thermally limited. You might find if you pass 8A through one, it will get too hot and die. Further on in the datasheet there are other specifications that also apply, so you can't simply say that the diode will pass 8A and survive. It would require heatsinking to achieve that value. As well, the 8A spec is 'absolute maximum rating'.