Giroud was facing his former club on the night.
Wenger told arsenal.com: "You always know with Olivier that you will get a guy who fights for the team. Technically it was not one of his best games, but after matches when you measure his performance it is [often] decisive. He had two assists here. Defensively he is always very reliable.
"Giroud is good when he plays completely on the offside line. Sometimes when he doesn't get the ball enough he wants to come deep. That is not his game. When he is a target man and uses his link-up play, he is fantastic because he can win in the air, he can score with his feet and can be a complete striker. He still has some work to do, but he is getting better."