I've not heard about the "stabbing mission" stuff? That would change things from fleeing the police to perhaps deliberate attack.
He certainly seems to be some very pro BLM, black nationalist type and doesn't like white people etc.. so perhaps it was a terror attack? though fleeing from police is a possible explanation too - albeit you'd expect most people to not simply ram through a parade.
On the long reddit thread it was said he stabbed someone (unrelated to the parade) and as he fled in the SUV he came to the parade. I guess his desire to flee meant he was going through that road no matter what, so he piled through all those people :/
The videos posted you can see various angles and the SUV literally makes a run for it from the left speeding all the way through at one point bouncing up in the air as he runs people under the wheels before it's gone out of sight in the far right of the frame.