Even in still air, the wedge of wind the front of a large truck causes can push a bike sideways. Then the rider overcompensates to recover. Hitting the side is classic for a close pass by a large truck. If it's windy, things are worse, because a truck can cut off a cross wind that the cyclist is leaning into, causing a swerve. The crosswind effect is bad enough to cause problems even for cars, and certainly motorcycles, which is why they're often restricted from bridges in NY when winds are high.

BTW - a truck doesn't have to hit the bike, and the rider doesn't have to hit the truck. The effect of a close pass can cause a cyclist to veer off the road onto the shoulder. When he recovers, he hits the burm, and it's like trolley tracks, causing the cyclist to fall into the road.

Back when I used to lead youth cycling trips,this was one of the top causes of crashes, with or without a truck. Cyclist goes off the burm, and falls when trying to get back onto the road. Note, this is especially bad because the cyclist will ALWAYS fall into the road rather than away from it.

Safely handling the burm was a routine part of pre-ride briefings.

BTW- nothing I posted should be read as meaning I think the driver did anything wrong, short of not being aware of the effect of his windage. It's very possible with plenty of room (over 5' mandated by PA law) and still have the same effect. I'll leave the assignment of responsibility to those on scene. This is just to say that the cyclist hitting the side of truck doesn't clearly point to either party being at fault.