Tao is certainly unique, but there's a lot of genius floating around and it can come in very different configurations.
I remember my first lecture in topology. Our professor said that while we may be smarter and beat our teachers in things like group theory and algebra, in this subject no one was going to be better than him. Experience also matters a lot in some subjects.
https://www.snopes.com/fact-check/the-unsolvable-math-proble...
I wonder how many other breakthroughs have occurred in a 'hard' problem that was thought to be 'easy'.
Probably happens from time to time.
I never saw it myself since I quickly realized I wouldn't cut it as a physics major there.
"After many nerve-wracking minutes of closed-door deliberation, the examiners did decide to (barely) pass me; however, my advisor gently explained his disappointment at my performance, and how I needed to do better in the future."
[1] https://www.ams.org/about-us/LivingProof.pdf#%5B%7B%22num%22... (found elsewhere in the thread)
"The rest of the exam then went fairly quickly as none of the examiners had prepared any truly challenging algebra questions."
Thus, he emptied the pool of questions prepared by the professors.
Notice that your quote does not really contradict a good impression upon the examiners. The nerve wracking is self reported, as is the word ``barely''. The later comments by the examiners may be also a generic sentence they say to everybody. Regardless of your level, you can always benefit for being told to do better.
Sure, if you ask these professors today they will probably say that they were very impressed by the young genius... but this does not really say much.