I can't find the thread right now, but someone else reported a similar incident a few months back. Unfortunately (or fortunately), the OP in that case had no idea what a "Hemi" was and was afraid he'd just been insulted somehow. So he asked the guys in the truck, and they proceeded to have a long conversation about car engines vs. bicycling horsepower.

He said it was the most pleasant driver-cyclist interaction he'd ever had, if I recall correctly.