I think the idea is that input is things that you absolutely, directly control, and output is more like "outcomes". You can control the price and certainly you can impact revenue by setting a price and, like, doing the whole rest of your job, but you still don't directly set the revenue.
My understanding of why they make this distinction is that if you focus on output metrics and you don't meet the target, you can be rationalize it as "well, we did a really good job but we failed to meet the goal because of circumstances beyond our control/market conditions/...", but if you focus on an input metric you're more directly accountable on whether you did what you said you'd do, and you come up with more actionable steps on how to fix it if not.
My understanding of why they make this distinction is that if you focus on output metrics and you don't meet the target, you can be rationalize it as "well, we did a really good job but we failed to meet the goal because of circumstances beyond our control/market conditions/...", but if you focus on an input metric you're more directly accountable on whether you did what you said you'd do, and you come up with more actionable steps on how to fix it if not.