Is a monster considered "destroyed" if I tribute it?
According to the official rulebook of Yu-Gi-Oh!, "destroy" means


  A card is destroyed when it is sent to the Graveyard due to battle
  between monsters or by an effect that destroys a card. A card that is
  returned from the field to the hand or Deck, or, that is sent to the
  Graveyard as a cost or Tribute, is NOT considered “destroyed.”


This can be found in the rulebook in the glossary part.

Even though Duel Links is a simplified version of the original game, it should follow the basic rules.