Yeah it's then too acidic for this specific one to grow. They must have found this by trial and error and a lot of ejected ordinance 
The original historical sushi was a fermented product like sauerkraut. Alternating layers salted rice and salted fish packed into barrels for months as a food preservation (like you would make salted pork).
Later sushi used vinegar to simulate the taste they had become accustomed to without actually taking the time to ferment for months. Like cheap store bought sauerkraut is usually not really fermented, just cabbage pickled in vinegar.
Truly fermented foods (rather than just pickling) are a magic health elixir. Builds incredible gut biome. Humans now don't get nearly as much fermented food as our ancestors ate.
Might have to try making historical sushi someday when I'm brave enough.
I was scared I'd poison myself first time I made sauerkraut but have never run into a problem. You'll know when there is a problem. Anaerobic bacteria have a whole different look and smell. Trust your nose. Millions of years went into that R&D.
