The additional 1 damage is dealt by the same source as the original source of damage. The damage isn’t dealt by Don’t Try This at Home unless it is the original source of damage. Note that while it is the source of damage for its activated ability, it won’t be on the battlefield as that ability resolves and its first ability won’t increase the damage it deals. (However, if it’s still in the graveyard at that time, it will count itself, as it is very much a hot card.)