In that case, at least he received a gentle warning in the form of a few days in the cooler, as opposed to wandering into the US where his attitude could have easily (depending on his skin color and other factors) have gotten him a sucking chest wound for his trouble.

Best to learn not to argue with people with guns at the border.

(Somewhat tongue-in-cheek here but I actually do think this is the purpose of aggressive border authorities. As someone who traveled around old, pre-EU, pre-Schengen Europe, you used to see it quite a bit there as well. Hard to say if it was intentional or just the product of different training, though.)