Bruno Guimaraes struck a disputed winner on Monday night as the visitors triumphed 1-0.
Areola told West Ham's website: “When you think about the game, we were solid all game, and we concede that goal.
“It's frustrating to lose like that, but it's what we did and we need to improve.
“I'm not a ref, the ref has a big job to do during a game. It's part of the game, we have to move on and stay focused and strong.”
Areola also produced a wonder save to rescue Max Kilman from scoring an own goal.
He added, "On the action, I thought it was the striker, but it was Max.
"During training, we've been practicing footwork and decisions and to be on the feet and to be ready to push.
"Lucky for me tonight, I've made that save. I'm happy with that save, but I'm frustrated about the result. It's always like that when you lose or when you don't get points. The team comes first."