The Gunners were up 2-0 at half-time but the hosts eventually clawed their way back to steal a point.
And Leno has revealed how his teammates responded in the dressing room after the final whistle.
"The distances between all parts of the team were too big so they had so much space, especially in the second half," said the German keeper. "It was too easy for them and they could go around our box.
"I don't know why it was like that but everybody could see that we have to talk about this. In the first half it was better but not perfect. I think we have to be honest and analyse this game. We were lucky we didn't lose.
"Everybody was angry and disappointed after [the game]. Everybody was emotional, very mad and crazy. But that is normal.
"The manager is a very positive guy. He said 'calm down and then on Tuesday we analyse this game and then on Thursday we have another game'."