Maybe they were coming from Quebec where they drive on the wrong side of the road... /S I wonder if others did not get that far. Attacking one border crossing out of so many seems odd, or they got their timing wrong.
Well, a casino in Niagara Falls, Ontario was mentioned. The problem with that thought is that there is a casino in Niagara Falls, New York maybe a mile or so from the international border. It would not have been necessary to cross a border if that was your objective.