Why Ender is upset after Salamander battle in Chapter11?

It is their second battle of the day, and Salamander was told about the battle far ahead of time and already was in ambush position. Ender has Bean openly tell Bonzo what he should have done. Ender also tells Anderson that next time, he should be given a good enemy. Ender thaws both armies and storms out without waiting for Bonzo's "dignified surrender."