"agreed upon deliverables" is one definition of output. I think he is talking more generally, e.g. lines of code, over-long email, unnecessarily verbose documentation, ..., I could go on indefinitely.

But you are really arguing in general against such lists like this, that don't "examine the nuance". But perhaps they are useful discussion point or memory joggers. And shouldn't the senior members of a team or managers explain to novices the importance of meeting such milestones that you mentioned?