just to give you an idea, how many dreams there must have been not to call it coincidence:
There are very roughly 250,000,000 US-Americans. Assume that each of them only once per life dreams about a plane crashing into a building. Assume that the average American lives 25,000 days (roughly 69 years) to make it easier. Then per chance alone, each night about 10,000 Americans have a dream about a plane crashing into a building.
Well, some may never have such a dream (that would make my 10,000 estimation too high), but a dream of that type a couple of day before it happened would still be called a coincidence (that would make my 10,000 estimation too low). Whatever the correct number is, it is in the region of several thousands.
Therefore, even with several thousand of such dreams there would still be no need for any other explanation than simple statistical coincidence.