Originally posted by galveston75
My question is..who was there hundreds of thousands of years ago to say they didn't?
Some other monkeys perhaps?
But your real question is "how do we know", or "how does Oprah know". Also, you have combined your question with an erroneous claim about knowledge acquisition.
It is not necessary for there to be a witness to an event for us to know of the event. In fact, witnesses are often not the most reliable form of evidence.
In this particular case, I would say it was probably:
a) a guess, based on the known fact that most monkeys do not do the same, so it is most likely that the practice started in that particular population at some point in time.
b) the known fact that the monkeys evolved from other animals incapable of using rocks.