I imagine it's similar to dry aging beef. With the right temperature and humidity, you support only bacteria that are safe to eat and you end up with a dry protective exterior before long which allows the fish to begin safely fermenting. You can do this with a surprising number of things. The trick is to have the correct initial conditions which prevents the proliferation of counterproductive bacteria. They also dip the fish in a brine to promote the right bacteria and prevent others from taking hold.

As for insects, it's likely that it's too cold outside (I think the article mentioned that it's kept outside in cool weather). Once it's done doing the cool weather thing it goes inside.