YouTube started to display videos from partners at the top of the search results and in the right sidebar. For some reason, YouTube likes to call these videos "featured videos". According to the help center, "featured videos will be primarily populated with videos from YouTube's thousands of partners, but might also include select user videos that are currently popular or that we have previously showcased in Spotlight Videos. (...) Featured videos are not advertisements or paid placements, but do feature content from partners with whom we have a commercial relationship."
I think the terminology is misleading and it should've been replaced with something more explanatory like "videos from YouTube partners". And just because the videos are from YouTube partners, it doesn't mean they're more relevant than the "organic" results. YouTube's parent company doesn't have a special section in the search results for websites from Google's content network.
Besides earning revenue from advertising and being promoted on every YouTube page, partners have many other privileges: they can upload custom thumbnails, create branded channels and offer downloadable videos.