Bird poop in the fermenters

I was talking with a brand owner about the process used to make his Tequila, and when he described his fermenters, I asked if they were indoors or outdoors. I hadn’t realized the regulations required them to be indoors – or, anyway, he said they did, though I found nothing in the NOM to corroborate that. But … he said they did because when you go around to these traditional vinatas, it was disgusting to see all the birds pooping in the fermenters. But … is it?