I see this happen often in Peugeot partners/berlingos and similar
The ECU gets moved, or the fuse box is pulled to access lower fuses. The ECU security casing can incidentally touch the fuse box battery lead, or a stray battery fuse board.
The ECU itself is earthed through a few earth wires, and the current will travel through these.
What will happen, is the pins will generally resolder themselves since there is zero resistance. After this, the ECU will not communicate. A quick dab with the soldering iron and it's good to go.
If the ignition was on when the ecu was shorted, you're in for a world of pain.
Thinking outside of the box is better than sitting in a dark one.