You're right that shock can be confused with stoicism. So can cowardly, weak fatalism. It now appears that the Muslim terrorist / "refugee" migrant, who was driving at 60 Kms an hour with a 25 ton steel load, would have driven into a food court-type area and children playzone if the truck's automatic braking system hadn't kicked in. But I'm a stoic. Check my face. Nothing. 

Obviously, panic, unless one's in an immediate fight-or-flight situation is always bad. But there's no substitute in this case for honesty. Honesty about Islam, about the depth and breadth of the threat and, only then, a rational response.