Believe that's what the article was about if you want, but I think the point is that there are always assumptions and it is better to be aware of them.
I assume the "he" above means Takamura not Threadgill. I think it is interesting that you are assuming what Tak's assumptions were. We don't know what Tak held in his mind, but given my distant impression of the man, Donny had no idea who he was playing with or what field he was playing on.
And isn't that the essence of winning? "If you know your enemies and know yourself, you will not be imperiled in a hundred battles." Sun Tsu
In that case, I'd play it more to luck then knowing. Anyone willing to engage in a fight like that is lucky to survive. The fact is he is damming Donny for using his assumptions, but he used the same assumptions to win the fight. (I'm going to fight 'dirty' and he wont because he thinks this is a sport.) Had Donny pulled a knife and gutted him, this story would of read a different way. Possibly used as an example of poor form in a challenge match by the author.
This is why I tell people there are two kinds of challenge fights.
Fights in the ring with rules. - These are healthy and safe ways to test skill and technique.
Challenge fights without the discussion of rules where one person is trying to prove something to another. - If you find yourself in this situation, both parties have made very grave and poor judgment calls. If a fight does happen, you must assume your opponent wants to kill you and you act as if this is the case. If you are smart you will realize you are being an idiot and simply leave the dojo and never deal with that person again. Anyone willing to fight without the safety of rules is simply too unstable to trust with your personal safety during instruction.
Further more, the lesson taught in my opinion did nothing to correct the students assertion. In fact it validated it. He stated the technique was outdated and unable to deal with the technique of today. The teacher showed no technique simply showed resourcefulness that in reality anyone could do with no training at all. This pointed out a lack in the students technique, but did not show the strength of the instructors technique. Nor does it validate the training methods. It would be similar to the teacher agreeing to the fight, pulling a handgun out, shooting Donny then stating his jiujitsu was superior. Unless he taught shoestring strangle from under the mount kata, he allowed him self to be bested, or was bested to make a point that did not address the students concerns. That combined challenging a student instead of just asking someone that disrespectful to leave really shows poor form.
I have never heard of this behavior in sport classes. I find it unhealthy.