Wenger's side returned back to fourth in the Premier League with Tuesday's victory at the Emirates, where Lukas Podolski's brace either side of Giroud's goal saw them to a come-from-behind win.
|7/1||Olivier Giroud is 7/1 with Paddy Power to score twice or more v Hull|
"He has gone through a difficult period as you know. I think it affected his game for a while and his confidence," Wenger told reporters. "You could see he was refreshed and he was up for it.
"At half-time he came in and was very, very down because he missed a great chance in the first half but he responded very well in the second because he is a mentally strong guy.
"When the team went through a bad patch there was a lack of confidence because some results went against us. The first to suffer are the strikers in a period like that.
"You have to slowly rebuild that [confidence] with results and resilience."
Matt Jarvis had given West Ham a surprise lead five minutes before half-time but the visitors were unable to hold onto their advantage heading into the break.
Podolski levelled a minute before the interval with a fine strike and Giroud had Arsenal ahead on 55 minutes after a superb first touch to bring down a long Thomas Vermaelen pass.
Ahead of a trip to Hull on Sunday, Wenger - whose team scored again in the 78th minute through Podolski - said the win was a key confidence boost for his team in the race to finish fourth.
"It improves the confidence of the team, Saturday and tonight improved our confidence," Wenger said.
"We have one advantage [on Everton]. The picture is very clear in front of us. We want to do it of course. It doesn't depend solely on us but there's a good chance if we win all our games we can do it."