Only a unit's target is considered to be engaged. If a unit deals damage to a non-target (for example, the Bow line has Volley which deals damage to an adjacent unit, and the enemy skill Necrotic deals 1 true damage to all adjacent units), the enemy taking the damage is not considered to be engaged. Other skills that trigger based off of being engaged, such as the enemy skill Shatter, would not be triggered if damage is dealt by a non-targeting skill such as Volley.
