Good thing the magician in the sky put the lorry there in the first place eh? Must have angered magic-dude somehow and he channelled his inner Loki. Like ants in a magnifying glass apparently.
Pretty remarkable damage and glad you came out unscathed. i have the Five model with the various bells and whistles. i have been glad a half dozen times or more that it has decelerated and applied brakes heavily without my input when i have been closing too fast on an object. it reacts faster than i can. the circumstances of your accident reminds me that the reason we see a heavy bar across the lower end of a trailer or truck, when approaching from the rear, is a direct result of the Jayne Mansfield accident.
My Five with ATP had saved me a few times when people cut in front of me unexpected. It works better in cruise control mode than pre-collision mode, which is usually too late and too little.