(Path of the Ancesteral Guardian Barbarian) Can you use Spirit Shield without activating Vengeful Ancestors?

Question

If I'm reducing the Area of Effect damage dealt to a friendly NPC by a PC, can I opt to not cause the damage blowback dealt by the Vengeful Ancestors?

Spirit Shield the guardian spirits that aid you can provide supernatural protection to those you defend. If you are raging and another creature you can see within 30 feet of you takes damage, you can use your reaction to reduce that damage by 2d6.

Vengeful Ancestors your ancestral spirits grow powerful enough to retaliate. When you use your Spirit Shield to reduce the damage of an attack, the attacker takes an amount of force damage equal to the damage that your Spirit Shield prevents.

Answer 1

Vengeful Ancestors does not apply to Area of Effect Damage

... because an area of effect spell is not an attack. And Vengeful Ancestors only kicks in when you use Spirit Shield to "reduce the damage of an attack".

The PHB on page 194 says this about how to determine if something is an attack:

If there's ever any question whether something you're doing counts as an attack, the rule is simple: if you're making an attack roll, you're making an attack

For an Area of Effect spell like fireball you do not make an attack roll, hence it is not an attack.

So yes, you can use Spirit Shield without triggering Vengeful Ancestors: Spirit Shield works against any kind of damage. Vengeful Ancestors only happens if the damage is from an attack. If its not from an attack, there is no blowback damage to begin with.

If the source of the damage was an actual attack instead of an area of effect spell, then you could not opt to avoid dealing the damage, because there is no language indicating it is optional. It does not say "You can have the attacker take..." it just says when you use Spirit Shield to reduce damage from an attack, "the attacker takes an amount of force damage".