Getting rid of someone because of a fuck up is amateur leadership (or politics to appease the mob). The relevant question is whether or not a decision was appropriate, given the information and parameters at the time of making the decision.

No one is perfect.

But why not then fire both parties was my question?

yes, CEO fucked up, should he now fuck up more by not firing them?

you come home from the grocery store, you bought frozen goods. you are unpacking, and think you're done, so you sit down in your couch to relax, a couple of minutes later you realize you forgot to put the frozen stuff in the freezer, do you just go "oh well i dun fucked up, nothing to be done here, i'd best just admit defeat and let my wife fire me from grocery duty"