That is not the point. By manipulating the Apple stock price the system sees and acts upon you can extract huge amounts of money. The actual price is irrelevant in this case.
There are many mechanisms of trading. Some use a couple different oracles and average(more complex but essentially that's what it is). In order to 'minipulate' the oracles, you would get eaten alive by arbitrage. If there's a difference across exchanges, HFT bots will equalize. Chain link takes that to the extreme and requires no oracle, only arbitrage. Since any arbitrage opportunity will be exploited, you can allow the active trading price and take that at face value. You can actually minipulate that price, by selling at a reduced rate but the thesis is that it would be economically disadvantages to do so.
