There are a variety of factors (I don't know exactly) that go into YouTube's ranking algorithm, including engagement, relevance, and the overall user experience. Some services may claim to be able to rank videos by manipulating these factors, but these methods are often against YouTube's terms of service and can result in the video being removed or the account being penalized.
In regards to ranking a video with only 400 views to the first position for a 20k volume keyword, it is unlikely to happen organically and sustainably. Typically, videos with high engagement, relevance, and overall user experience will rank well on YouTube, regardless of the number of views.