Giroud scored twice in two minutes just before the half-hour of the side's fifth-round tie against Middlesbrough, setting up a 2-0 win, and Wenger believes both goals were the product of the player's evolution as player.
"I believe Giroud is a different player from the guy who arrived here," Wenger said.
"He understands what top-level football demands, works with great concentration in training, improved on his mobility, technical quality. Of course his body is very strong and he uses it very well."
It was Giroud's movement that saw Arsenal finally open up Middlesbrough on 27 minutes, as he got behind the defence to stab in Kieran Gibbs's pass, completing a move that involved every player in the Arsenal XI.
The second, just two minutes later, involved quick-thinking as Giroud reacted to Alex Sanchez's quick corner before anybody and volleyed past Tomas Mejias.
"The first goal is what we tried to do in our build-up," Wenger said.
"The second goal shows the game belongs to the players as well. It's a consequence of two players who respond quickly to a situation and analysing quickly what they want to do well. That's basically what it was, a consequence of intelligence and technique."
Wenger believes the strong team he picked indicates his strong desire to defend the FA Cup, as he revealed Alexis Sanchez was again eager to play, despite expectation he might be rested.
"Alexis became string as the game went on. I took a gamble, and took him off with 20 minutes to play.
"He always wants to play. Everybody is like that, but he is bit more like that. He didn't miss too many games.
"What was important for him was to get through without injury."
New signing Gabriel Paletta also came through his first start for Arsenal with a clean sheet, showing his aggression with one industrious foul that prevented an Adam Reach run on goal. Wenger praised his contribution, and said there is "a lot to come" from the defender.
"It was interesting to observe Gabriel today. His first game in a cup game which we had absolutely to win, he showed important qualities, great concentration, great urgency to defend, good pace, especially on the recovery tackle he made in the box.
"He played a little bit with the handbrake because he didn't want to make a mistake.
"From what I've seen, there's a lot to come."
Aitor Karanka meanwhile said he "didn't like anything" about Middlesbrough's first-half performance and that he was disappointed in his side's performance.
The Spaniard said the victory over Manchester City in the fourth round might have made his players think the game would be "easier" and that they were far from the "perfect" level shown at the Etihad.
"If you want to take something from games against Arsenal today, you have to be perfect, like at Etihad Stadium and you have to take advantage of your chances. If you make mistakes, it's difficult.
I don't know if it's frustration. A little bit disappointed because everybody was expecting a game like against Liverpool or Man City. This is my biggest concern. We didn't go to the pitch in the way we usually go,. The second half was better, but the first half I didn't like anything."
