Projectile Damage + Explosive Spear

I am experimenting a bit with Explosive Spear. Surely, projectile damage affects the damage of the projectile when it impacts an enemy, but what about its explosion?

I have searched online about this, and I am getting mixed results. Some say it does, while others say it doesn't, as it is an explosion rather than a projectile hit.

When adding some Projectile Damage nodes, it feels like the explosion does more damage. Does it actually affect it, or maybe Area Damage does?

It does.

It doesn't if it's separate attack that originated from something and is diffirent type. Like volcanic eruption.