You are right. A big airliner like the Boeing 787 fully loaded with passengers, luggage, freight and fuel would require a lot of runway to get that big plane up in the air. It's all about having the correct speed for takeoff, which is figured by one of the pilots inputting the correct numbers into the on-board FMS (Flight Management System) computer.
I think the pilots in this video may be going through a qualifying or validation flight, which is a flight to make certain that the plane is doing what it is supposed to do. When I flew out of John Wayne Airport in Orange County, California, I had to quickly climb at a steep angle because they have a noise abatement rule in place that because we took off over a housing development, we had to get up very quickly to lessen the sound (noise).
I have toured one of these Dreamliners, but have never flown in one. It is, however, on my bucket list to do so, but I want to fly it in First Class.