Oh, it was no-one important. Only Craig Federighi said it...
I think you are misunderstanding what he said. He said that closing all apps from the multitasking all the time won't help with battery life because iOS already have a really good multitasking management, it automatically put apps on hold when the user don't use them which help preserving battery life.
He never told anything about the Facebook app which is a completely different story.
The App Store have a very strict policy about approving apps that are allowed to stay in the background and apps that are not. The only apps that are allowed to stay forever in the background are apps that need to use Voice over IP (mostly apps that have a buit-in calls feature like WhatsApp or Messenger) in order to work properly. iOS will never stop background activity of these apps because otherwise it would interrupt the call.
The Facebook app use Voice over IP for no reason at all (because the app doesn't use it and doesn't need it anyway) to stay forever in the background and that's why it's killing the battery life. Closing the app every time you don't use it stop that background activity and help improve battery life.