Looks like I don't understand how things work.

I thought police file initial charges ... they just do the arresting.

I've been driving for a number of years. I've seen people doing their makeup, eating, trimming their fingernails, shaving, and reading (all before self driving cars were a possibility). And of course, drunk, drugged, driving while exhausted, or texting are all a possibility.

It is unlikely that the truck driver drove into the cyclists without at least knowing that they were there, but there is a possibility that he was just unfit to operate a motor vehicle.

Edit: just to add ... as a cyclist, I've been pushed off the road by drivers, and I've had a tanker truck blow their horn at me while passing mere inches from my handlebars at 60mph ... fuck cars, but I'd like to hope that most drivers aren't out to kill us for not driving.

I'm not sure which is worse: doing it out of anger or out of complete disregard

He's also being charged with three counts of aggrivated assault (basically intentionally attacking a person with a weapon , most likely the truck in this instance).

Charging him with assault should require intention. Of course police file the charges, and the prosecutor can amend them as more details come to light. There isn't exactly a lot to go on in the reporting I've seen.

I hope this isn't a case of road rage or intentionally targeting a large group of cyclists. I don't like losing my faith in humanity, but I can't just write this off as a tragic accident either.