Giroud was dropped in midweek for the Gunners' defeat to Bayern Munich in the Champions League, but he scored two goals at the Emirates Stadium on Saturday as they earned a 4-1 victory against the Black Cats in the Premier League.
"I had no hesitation about his strength of character," he told the club's official website. "Of course you want him to come back into the team and be successful, which he was today because he scored two goals.
"One great one at the end of great movement and the other a little bit of a gift from Sunderland. He got an assist as well, so he did well."
Arsenal continue their Premier League campaign next Saturday with a trip to Stoke City.