Ok, I don't understand this part then: "With RED the router will instead have some probability of dropping the packet based on the size of the queue, going up to 100% if the queue is full." - that seems to be universally true for any queue with limited capacity. If it's full, it's going to start dropping packets - whether it's those on the queue, or the new ones doesn't matter. Any queue which is full will require dropping as many packets as the number coming in.
Is there some reason this was described as a specific behaviour here?