[Non-Sequitur]

But suppose you call the cops and falsely claim there's a terrorist on the loose in a train station, inciting a stampede of confusion. You should be personally liable for making that false report.

A more correct analogy would be if you called the police and falsely claime there was a terrorist, and then the cops arrived and precipitated the stampede. Regardless of what the Costco employee may have said on the phone, there was no panic or stampede, nobody got injured or killed until the police showed up and apparently badly mismanaged the situation.

[conimbricenses]

The point is that the cops showed up thinking there was a crazed gunman "going berserk" in the store because they had apparently been told that by the Costco employee. When they arrived common sense should have kicked in as soon as they realized there was no gunman. But the Costco employee is also at fault for the way he/she described it to them.

To put it another way, it is not unreasonable to think that this would have ended very differently if the Costco employee had called the police and said "We have a man in our store who claims he has a concealed handgun license but we're not sure. Could you send somebody over to verify it?" I don't underestimate the ability of police to botch that up as well, but it would have likely produced a much less tense situation than "there's a guy with a gun going berserk in our store!"