Just after you've been fighting for a while you stop getting randoms, because combat without bone burying doesn't trigger random events. That's why an auto fighter can run 24/7. When you stop fighting you need a random because you haven't had one in a while and the first trigger you do (Burying a bone) will trigger a random.
He nailed it. Fighting does not generate the potential for a random like bone burying does. After being on for a while, the bone burying will generate the overdue random.
Try it yourself! Kill stuff for 30 min without burying bones. Then bury a single bone. You will get a random most of the time.
These are my principles. If you don't like them, well... I have others.
Since brevity is the soul of wit, I will be brief. Auto Correctly.