This is a Topic worthy of its own discussion.
The point is that when two dissimilar metals are in electrical contact with each other then corrosion will occur.
The rate of corrosion is accelerated, the further those metals are apart on the corrosion chart.
Adding and electrolyte makes those corrosion conditions more favourable.

Key factors: Dissimilar metals, Electricly connected, Electrolytes.

Contecting two dissimilar metals with a conductive bolt and immersing is salt water satisfies the above conditions.

This is my understanding of the situation, and I crave more understanding.