This is because the dissimilar metals have different electrode potentials.

Any junction of dissimilar metals will produce an electric potential related to temperature.

In the case where it is caused by dental work, the dissimilar metals used may produce a measurable current.

When these dissimilar metals combine with saliva, a battery effect occurs.

The potential for electric current is contained when these dissimilar metals come together.

Galvanic can happen whenever two dissimilar metals contact each other.

Magnetic pulse welding may be used to join dissimilar metals.

"How does he manage to join these two dissimilar metals together like this?"

The driving force is the difference in reduction potentials between the two dissimilar metals.

Forge welding is versatile, being able to join a host of similar and dissimilar metals.