Try this search:
http://www.google.com/search?hl=nl&q=interessant

The #1 result is a site that has a thumbnail although there is no movie or anything video releated available. How great would it be, if you don't have a video site, but you can push a video thumb to your SE listing. Does anybody have an idea how this happened?

There is the same story here, on Google.NL too:
http://www.seroundtable.com/archives/016325.html
Bug? Spam?

Google found a video embedded in that site and decided it makes sense to consider it a video site. There's probably a bug in the video site detection algorithm.

But making use of that 'bug' would be very interesting :)

But since millions of pages have a youtube vid embedded (or any other source) how come they dont have a thumb, since this site isn't hosting anything (or featuring something related to the thumb).

Indeed interesting mistake ;)