fat is rendered anytime the cut of meat is cooked in any kind of container and the fat liquifies and then resolidifies after cooling.  Roast a chicken in a clay pot and the fat will do just that.  When cooled (to room temperature) it forms a substance like soft butter, to lower temperatures as it would be outdoors in winter, to a harder consistency.

In other words, fat plus any kind of container plus fire are going to allow the opportunity to collect rendered fat.

Anecdotally, I was certainly under the impression that bear grease was collected and used for a variety of things by native americans. What would that be except rendered bear fat?

Kathleen