Oh, so the 'debunking' is not on whether or not an attempted mass murder/arson occurred, but that there is no "direct linkage" between the occupation and the crime.

What that likely means is that they don't know who the people in the video are. It seems pretty likely to me that it's related to the occupation, especially since there was a 'confrontation' earlier that day with residents of the building. It's not like buildings are burnt down in Ottawa every day.