Is it normal to have 9 versions of the same thumbnail? There’s a main one and 8 others of various sizes, like all-trailers-for-gta-5-2-youtube-thumb.jpg, then all-trailers-for-gta-5-2-youtube-thumb-480×272.jpg and others.
Yes, when you upload an image to media gallery, WordPress automatically creates all registered sizes by cutting from the full size image.
Also, I take it the scrolling between the embed and featured image like on http://www2.wikigameguides.com/angry-birds-star-wars-2-p2-s2-3-star-walkthrough-escape-to-tatooine-level-p2-s2 is a theme problem?
Technically, when you import a video as theme post, all the plugin does is set the content, title, image, post type etc in database. After this, it doesn’t interfere with that post anymore since the theme deals with displaying it and everything else. So yes, it has something to do with the theme.