Hoarding groups called whales can affect how the market goes by pumping and dumping. This had been happening in alts not sure though on BTC since there's a big amount of money involve because of the price.
The same thing goes to btc as well, couple days ago the price's pumping quite high for a short-time and suddenly drop red in just a few hours. The whale's real for sure, but we don't know whether they intend to "maintain" the market price or not. Safest way is not to buy while it's still low.