But this is quite literally a situation where a person shouts about a fake threat so as to cause alarm in a crowded fora -- the article does not seem to argue that doing so would be legal or that it would not be a permissible restriction on speech.
So I defer to anyone who knows more than I do about speech law -- to be clear, it is still impermissible to (falsely) shout fire in a crowded theater, right?
The underlying point is that, it's a complicated topic that is not easily answered. This is like saying "Shooting someone is illegal, right?" Well, it's complicated. You have Murder 1, Murder 2, (sometimes more), Manslaughter (Voluntary, or Involuntary), and you have shootings of self-defense which are legal. It entirely depends on the circumstances under which you shout "Fire!" and the outcome of that situation.
There are legal principles involving whether or not you caused harm, whether or not you intended to cause harm, whether or not you reasonably knew it could cause harm but proceeded anyway. These questions will have outcome on which charges are applicable, if any are at all.
Should you shout fire in a crowded theater, and folks stampede. Expect to be charged for inciting a riot or at least disturbing the peace. Should nothing happen? You might be asked to leave and not come back by staff and have a no-trespass order, you may even get picked up on a disturbing the peace charge. One of the "You can beat the rap, but you can't beat the ride" situations.
It's a complicated and, IMO, interesting topic.[0][1]
[0] - https://www.popehat.com/2012/09/19/three-generations-of-a-ha...
[1] - https://legaltalknetwork.com/podcasts/make-no-law/2018/06/fi...