If he hit a "chunk of a truck tire" then I'd wager that means blowout or tread shear - either way those bits of metal and rubber are more than capable of killing a human being dead or going right through a glass windshield/window. Not a small amount of energy potentially slammed into the CTS, so honestly I'd say it did okay, considering all said and done.
I'm also amazed C&D didnt complain about the repair bill - that said I'd wager the clips, parking sensor, and the LED marker light didn't need replacement. Additionally, at that price for the headlight, they got the entire assembly with drivers and all - you can actually order parts of the sub assembly (but again, the shop is likely trying to get every dime, especially when they know the car is from a magazine that won't just pay every dime they ask for - they'll happily overpay.
C&D also lacks the skill and knowledge to show the damage under the hood, which is where a lot of that labor came from.