Goals from Odion Ighalo and Adlene Guedioura dashed the Gunners' hopes of becoming the first club since Blackburn Rovers in the 1880s to win the competition three years in a row.
Arsenal suffered their 13th defeat in all competitions this season, three more than last campaign, with at least 10 games left to play.
"It is the best time to play Arsenal and we came to the match very confident. When you see Arsenal playing against big teams, they look like a small team," the former Tottenham Hotspur keeper told ESPN Brasil.
"They don't look like winning a title soon. We knew once we had the ball we'd be able to pass it around since Arsenal gives you too much space. They are not strong defensively."
Arsenal are third in the league, eight points behind leaders Leicester City, who play Newcastle United on Monday.
They trail Barcelona 2-0 going into the Champions League last-16 second leg in Spain on Wednesday.