Should anyone who owns a lot of bitcoin affect the bitcoin price? Is this situation artificially manipulated?
Should anyone? No.
Can anyone? Yes, definitely. Market manipulation requires quite a lot of bitcoin, though!
The best thing to combat price manipulation is the global distribution of this market place. There are people on nearly every continent that are investing, hodlers of Bitcoin. This makes it much more difficult to manipulate the price but the possibility of it happening can never truly go away. That said, it only takes victim that people that buy or sell into it. If you keep holding (even if you're buying into a slide or run up) you maintain control of the price you've locked in.