Firja, Judge of Valor - Doesn't destroy non-fetched cards

Firja, Judge of Valor
When you cast your second card each turn:
Pick on of the first 3 different cards from your library.
Fetch that card. Then, destroy the others.

Plargg, Dean of Chaos
When this creature attacks: Discard the last card without mana from your hand, then draw a card.
... other text, not relevant to this issue ...

So if I trigger Firja (play 2 cards in a turn) and pick a card (from the next 3 in my library).
The chosen card goes to my hand, the other 2 cards do NOT go to my graveyard.

I have confirmed they aren't moved to graveyard, since I have Plargg in play.
He attacks and his ability triggers, to discard the last card without mana (the one i picked via Firja)
Which is discarded, and I draw the next card which was visible when Firja's ability triggered previously.