Hello Exothermic,
there is no need for this to be added to the rules or the kos reasons. It is indeed a valid kos reason, we only listed a few examples of accecptable and unaccecptable reasons to give a rough Explanations. There are a lot more KOS reasons not listed on the list in the rules, only because if we would add them all the list would never end then.
As you can see we only have only a few and this scenario you described is also a valid KOS reason (Why would we have "Obstructing the diamond ore from reaching the furnace" as a valid kos reason and "Obstructing the Diamond block from getting to the chest" not as a valid kos reason, thats would honestly just be silly).
However you might wanna tell me that staff member name that punished you for killing the guy in this situation that I can have a little chat with them