Basically, stock markets are based on predictions. If it is likely a stock will continue to fall, it is called a drop. You can not know if it’s a dip or a drop in advance because rising and falling stocks are always relative to the rest of the environment. So calling it a drop would be not wrong, but an unlikely prediction.
Generally, “dip” carries the connotation that there will be a rebound, or a return to the original position. A “drop” however would mean that this would hurt the company in the long run.