The algorithm is not as advanced as people think and can easily be 'cheated'.
The search results are mostly based on the most popular search queries of all users and engagement on that content. (this is how stuff like iPhone, Brexit, Trump and yes Hitler and Nazi's get so much traction on YouTube).
For people with little to no search history this is actually the most important factor. Already popular search queries get an extra boost in all recommendations and engagement on say Nazi content is fairly high.
So if people write anti-Nazi comments or release reaction videos specifically aimed at attacking Nazi's they are simply boosting all the Nazi-related content.
In a way, punching a guy like Richard Spencer and having it go viral helps with the overall visibility of all Nazi content.