Blastfire Bolt deals 5 damage to target creature. Destroy all Equipment attached to that creature.
Blastfire Bolt can target any creature, not just one with Equipment attached to it. The damage will be dealt to the creature even if it doesn’t have any Equipment attached to it.
If the target creature is an illegal target when Blastfire Bolt tries to resolve, it won’t resolve and none of its effects will happen. No Equipment will be destroyed.