It can be said that way, because bitcoin is the main coin or it can be said that bitcoin is the oldest coin. Although bitcoin prices are currently down it does not need to worry because over time bitcoin prices will rise little by little.
Only thing required in case of bitcoin investment is lot of patience. If a person has the patience to wait for at least an year after investment, he will never be in loss. Most of the people who make loss on their bitcoin investment are those who sell in panic where there is sudden fall in bitcoin price.