Simultaneous Damage

[unemployer]

Hi all,
Just had a questions regarding Pyrokinesis
Player 1: Just played a 2/2 Knight of the Relinquary with 1 land in graveyard (3/3) and a Dryad Arbor in play
Player 2: On the main phase, casts Pyrokinesis and targets the KOTR for 4 damage.
After the game, I argued and said that Player 2 should have targeted KOTR for 3 Damage and 1 damage for Dryad Arbor. Player 2 said that the KOTR will grow if Dryad Arbor dies. I argued that since the card Pyrokinesis hits both creatures simultaneously, they both die. Which one is correct?
Reference
4RR - Instant
You may exile a red card from your hand rather than pay Pyrokinesis's mana cost.
Pyrokinesis deals 4 damage divided as you choose among any number of target creatures

[Justin]

You are right. Creatures dealt lethal damage by spells such as Pyrokinesis die at the same time.

[Julian23]

Said "same time" would be when state based effects are checked which is right after Pyrokinesis has completly resolved and right before any player would receive priority. When the game checks for state based effects, it sees a 3/3 creature with 3 damage on it and a 1/1 creature with 1 damage on it. It performs the corresponding action, which is putting those creatures into the graveyard.