"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.