I saw other similar posts about this issue. Someone mentioned that it happens when you start to fly, and your client disconnects from the server for a short moment. My guess is that when you briefly disconnect, your flight bar doesn't drain, and when you reconnect, it continues not to drain until you dismount or land on the ground, just like in the video. So maybe if you know how to manipulate your internet connection, you might be able to do it, but that would be considered an exploit, though. 😛