The KML you flew from is not the same as the data acquired during the scan. Due to the wide angle of your LiDAR, the scan area is always larger than the flight plan.
The ROCK Cloud uses a very sophisticated and accurate way of determining the area of your point cloud. On our servers we load all of the points from every file into a 2d plane and draw a border around the dataset. If you have non-contiguous point clouds (think Islands), then multiple borders around the contiguous islands of points will be drawn. Once all of the borders are created, then the area is added up and reported out.
Why is my KML or Flight Plan so much less area?
Simply put, the angle of your LiDAR sensor means you collect a lot more data than directly under your flight plan.
One way of verifying this yourself is to: