The Gunners manager told the club's official website: "I spoke with Giroud. He said to me that he slipped at the moment he went for the ball and it's confirmed by the television.
"I haven't seen it but he's not a tackler. He went over the ball and knowing that Sidwell had been sent off before, I had no illusion of the colour of the card.
"Sidwell's challenge was in front of me. I've seen that better. I think the referee had only the red card to give."
The result leaves Arsenal third in the Premier League table.