If the wheels are driving the prop, and the vehicle is stationary, then how can it start doing anything.
The bluff drag of the device in the wind is enough to start it rolling and then the process starts from there.
Here's a video of an early run where you can see no one touches the device as it starts.
YouTube - BUFC very first run
I just submitted a post with a link to a video showing the vehicle self starting as described, but apparently the link caused the post to go for moderation. Hopefully it will show up eventually.
For info, new posters (I think until 5 posts or thereabouts) are moderated regardless of content across the site. Creates a problem with an interesting thread where posts accumulate quickly .. due to the need for a mod to be able to review and OK the post. Fortunately, for OK posters, the nuisance is short lived and goes away fairly quickly. Posts now tidied up and the video link visible.
Needless to say we're all fascinated by the thread and, as another sailor has indicated, the basics of getting something for not very much from the wind is well established .. now, if I can just get my trailer sailer to go faster I might end up becoming competitive ... - John