cell() doesn't stand for any value. It instantiates (pre-allocates) a cell array of empty contents - one empty cell for each of the files you found. I think if you read the FAQ you'll have a better idea of how cells work. ?
importdata() can bring in who-knows-what, so that's why we need a cell since each cell can contain something completely different, unlike other arrays. If each dataset is the same size, shape, and class, then you might use a double array to hold everything instead of a cell array.
