The video you linked to doesn't show anything. It suggests Rittenhouse was acting as a "rooftop Korean" protecting businesses, but obviously he wasn't qualified to function as armed security.
Then it asserts that because the people shot were white, Rittenhouse can't be a white supremacist. Myself I have no idea what his politics might be, but recall that being a white supremacist didn't stop James Alex Fields Jr from killing Heather Heyer in Charlottesville.
At no time does the video provide evidence that Rittenhouse started shooting because he was assaulted by protestors.