That's not exactly how I understood the explanation at Braukaiser. I think the author there is saying that yeast does well in a low-pH environment, and yeast is able to lower the pH of the wort itself. However, if there is lots of wort and not very much yeast, there isn't enough yeast to be able...
It's because the yeast has to lower the pH of the wort before it can properly start taking up nutrients. If there's a large wort-to-yeast ratio, that is a more difficult task.
There's an excellent explanation here...
If your sanitation is a bit off, perhaps the source of contamination could be the yeast from a previous batch or maybe a current batch?
You might be lucky.
Don't worry, it will be absolutely fine, just like your man said. Five to seven days in the warm, then about four weeks in the cool before drinking it works for me.
Plus they had to do it against an outflow of carbon dioxide coming the other way. The beer will be fine, totally 100% guaranteed.
I went on a brewery tour last year and was amazed to see that fermentation on a commercial scale is open to the air. The beer ferments in huge vertical cylindrical...