An entire country's grid goes down and you figure they instantly understand the root cause?
3 countries. Spain, France and Portugal.
However, not entirely. The islands in the Atlantic and Mediterranean were not affected, and most of France was fine.
So as you said, we cannot know what happened but we can begin to understand and eliminate some potential causes.
The Chinese anchor theory is not looking great right now.
An IT problem that starts in Spain and interferes with Portugal mainland grid leaving out the islands is very odd.