The effects of "Grapha, Dragon Lord of Dark World" are not treated as resolving simultaneously. First you select one card on the field and destroy it, and then you look at one card in your opponent's hand, and then (if the card is a Monster Card) you Special Summon this card to your field. Thus, after resolving the whole effect, it is treated as "when a monster is Special Summoned".
Suppose that this card is discarded by an opponent's card effect. If you cannot destroy the targeted card, then neither look at one of your opponent's cards nor Special Summon that card.
Dark World Rulings
Judge Program Forum Rulings
These Ruling(s) have not been confirmed as applicable to the TCG.[Notes 1]
If you discard from your hand because of the effect of a "General Raiho of the Ice Barrier" your opponent controls, then it is treated as you discarding from your hand by the effect of an opponent's card.
These TCG rulings were issued by Upper Deck Entertainment and have since been deemed unofficial by Konami. They were previously considered official, but may or may not necessarily hold true nowadays.
↑Konami Judge Program Rulings are considered unverified, as their source(s) are not publicly viewable. They are not confirmed as applicable to the TCG until they have been officially published by Konami.