Would you have thought it was a penalty?

Australia are on the attack and go right. Scrumhalf Will Genia has two Australian players to his right and gives the ball to David Pocock (7). Saia Faingaa is ahead of Pocock and blocking Jaque Fourie from getting to Pocock who makes contact with Faingaa as he goes forward.

Clearly there is obstruction and play cannot go on. But why a scrum?

Did Faingaa try to block Fourie? It looks much more likely to be a case of bad timing - if even that. Genia could have passed to Faingaa who was in the position to receive a pass. Faingaa was not there to obstruct.

The referee awarded a scrum, citing accidental offside.

Law 11.6 ACCIDENTAL OFFSIDE
(a) When an offside player cannot avoid being touched by the ball or by a team-mate carrying it, the player is accidentally offside. If the player's team gains no advantage from this, play continues. If the player's team gains an advantage, a scrum is formed with the opposing team throwing in the ball.

It certainly seems the right decision.