The video released by Vandenberg AFB begins in infrared light, so the bright parts would represent heat from the X-37B's descent into the atmosphere. Then it switches to normal light, which is not very bright since it is ten minutes to six o'clock in the morning at the Pacific Coast base. Note that the plane is only 9.5 feet (2.9 meters) tall and 29 feet (8.9 m) long, with a wingspan of 15 feet (4.5 m). Its payload bay is about the size of a pickup truck's bed. Boeing has done some study for a larger X-37C, which could be configured to carry a crew of 6 astronauts in low earth orbit.
More photos and graphics of the X37-B can be found here.