The ARRJ and Akira are both correct with this ruling. Here's who it looks basically broken down.
Airknight Parshath attacks.
Fiber is flipped and the effect is ACTIVATED.
Enter Damage Step.
Damage Calculation is first, Fiber Jar is considered destroyed during the damage calculation and the owner of Fiber takes damage due to Airknight's effect. Airknight's effect then activates after dealing the damage, allowing the player to draw a card from their deck.
Then Fiber Jar resolves in the resolve effects part of the damage step, sending all cards back to the deck (excluding rfg cards) and the deck is then shuffled and both players draw five cards.
If the old ruling was still in effect on the card, then there could be no damage calculation and you couldn't draw. It makes no sense to have damage calculation when there are no long monsters on the field if Fiber were to resolve first. Remember, for damage calculation to be met, both monsters still be on the field. So the old ruling didn't even make sense in the first place with the entire breakdown of the damage step and the Airknight VS. Fiber (or Cyber as well) rulings.