I am in the criminal law field, not civil, so my experience is not based in liability but rather criminal culpability. So I have no direct experience. Also, I've never seen it come up in a criminal matter either.
However, I'll point out that I was surprised that a lawyer is so quick to speak in absolutes. We tend to not do that. That's why we answer questions with "it depends" so often.
For instance this statement from the article:
No. The lawsuit against you will be dismissed and will need to be brought against the attacker with the knife. You are free from liability under the doctrine of transferred intent.
It states that the lawsuit will be dismissed, and you are free from liability. Well maybe it will, and maybe you are. But the judge may let it go to the jury. If this is the case, it may be overturned on appeal, but not until after a long and expensive process.
Be careful of absolutes. If a lawyer guarantees you a specific result, you should probably find another lawyer.
In the Restatement of Torts that the author cites, it gives and example of an exception to this doctrine.
A points a pistol at B, threatening to shoot him. B attempts to shoot A, but his bullet goes astray and strikes C, an innocent bystander. B is not liable to C unless, taking into account the exigency in which A's act placed B, B fired his self-defensive shot in a manner unnecessarily dangerous to C.
Restatement (Second) of Torts § 75 (1965)
Again, be careful of absolutes. The author gives an absolute, then later in his article, cites an exception. Well if there are exceptions (which is nearly always the case), then it's not an absolute.
Words matter.