Saw this on the news last night. Apparently the lorry was parked on the side of the road, the car had rammed into the back of it. The impact forced the lorries to move forward and bring down a post as well. News did show the vehicles, looked like the car had run under the lorry on impact, the roof was almost flat with the doors.
I drive past Seeduwa daily, saw no visible signs of an accident on the road when driving back home last night. Didn't see anything (like a fallen post) this morning either. Anyways, that area is very popular for lorry & container truck driver to stop for a break, on the side going to Negombo. It's also very crowded with people crossing etc. Very likely, the car was trying to avoid someone turning right without any prior warning or a pedestrian. Both of which happen regularly on the Negombo-Colombo road.