I think who provoked whom is a bit orthogonal to the dicussion though there is definitely merit in knowing the history accurately.

If one considers that Kim Il Sung with the help of USSR and China defeated Japanese colonisers, then the USA swoops in and reinstates some Japanese and their Korean collaborators to positions of authority in their half of the split, I think it would make sense if North Korea invaded without provocation. No blood was spilt by the Americans in the process of Korean liberation directly.