+1 on the mirror.

I learned to drive in Amish country in Ohio. One of the things drummed into us was how slow horses and buggies are actually traveling. If they don't pull off the road you must pass them (or not) as if they were cars, but make up your mind as soon as you see them ahead of you because you catch up in no time. It sounds to me like the truck screwed up--should have pulled out to pass earlier or not at all, and should have gone all the way over the center line. That would have revealed your presence to the SUV and deterred the SUV from passing the truck while it was passing you. Instead, the truck must have slowed way down (but not enough) while thinking about what to do. Whenever you have to think about what to do you become unpredictable. Hence the honking. Not much you could have done about it all, but a mirror might have helped you keep track.