The difference between a sacrificial altar and a butcher shop / BBQ joint is the words people say when they're there, and the article says that culture didn't have writing. If the person in charge asks the customers what favors they want from the gods, it's a temple; if they ask whether you want regular or extra crispy, it's a BBQ joint, and in some cultures they're going to thank the gods for the life of the animal even if it's a BBQ joint. In a temple, it's more likely that some parts of the animal will get burned instead of eaten, and in a BBQ joint, it's more likely that there'll be spices on the meat, and maybe priests get paid a bigger share than a butcher and cook, but none of those are universal across known cultures.
Also, the article says it was a two-story building; just because it's underground millennia later doesn't mean it was underground at the time.