I don't mean burnt into the video. The YouTube inteface says "auto-generated" when it is the case (example [0]). Sometimes, though, it seems that uploaders have taken auto-generated captions and added them as if they were manually made, so then YouTube doesn't label it correctly.
Ok, I never noticed that. I just read the captions and assumed obvious misspellings were auto-generated.
For example in this video[1], the caption text is "L1D cache misses" but he's actually saying "L1-dcache misses". (The Linux terminal screen he's showing does display "L1-dcache".) Even though that video is not labeled as "auto-generated", I assumed it was because of the bad caption. Based on your info, I guess CppCon uses humans like Mechanical Turk or other non-domain typists to manually add the captions.
Manual captioning is almost always not done by domain experts, but by people who have some training with a captioning system and work as professional captionists. Their main advantage is that they'll caption much faster and much cheaper than having domain experts do it, but the quality tends to suffer.
In college, I met a deaf guy who always had two women accompany him to lectures; one of them would repeat everything into a mouth-covering microphone to generate an automatic transcription and the other went over it to correct obvious errors. They generated a lot of nonsense, especially when the German professor was using some English loanwords for CS concepts. I was always amazed that the deaf guy still somehow managed to learn something from these garbled transcriptions.
[0] https://www.youtube.com/watch?v=om6HcUUa8DI