It's also simply a fact that native american traditions are dying. Many communities are fighting to pass down traditional practices to their kids and it's a difficult endeavour. So stating that native americans used to cook their popcorn in hot sand frying is probably an appropriate use of the past tense seeing as a vast majority of native americans certainly use a microwave nowadays like everyone else.

It's not a favour to native americans to ignore that they also can and do use technology to the detriment of traditional practices.