Google has been giving preferential treatment to their YouTube videos for some time, especially for non-competitive search phrases. The title and tags that you use are critical factors.
I have tested this a few times myself with similar results. One thing that I have also seen is that a YouTube video does not seem to hold the top slot for very long unless it starts to pickup Views and Likes. If it doesn't get these, it is easily knocked out by a newer competing video. Let us know if you see the same thing.
"Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote." -- Benjamin Franklin