I mean, quite obviously the indigenous peoples of the Americas were the first to discover maize, and learned how to grow it, grind it, nixtamalize it, and cook it.
...but did they pop it? I mean, it seems like they had all the ingredients and know-how to do it. Fire, little bit of cooking oil, corn kernels.
Short answer: Yes. You also don't need oil if you're popping in a vessel that allows the kernels to move constantly, like my air popper. Source: I've never poured oil in my air popper. I've also cooked it in a skillet over an open fire.
Longer answer: The people of the Americas didn't just discover maize, they bred it from an earlier, barely recognizable plant called teosinte. One of the varieties that developed over the centuries was the variety used for popcorn, and they did indeed pop it. Popped kernels have been found in New Mexico that were perhaps 5000 years old. There is evidence of popped corn from Inca settlements to Aztec and up to the Iroquois, and while it might not be true that one of the Indians that dealt with the Pilgrims brought a basket of popcorn to dinner (despite the high mark that a paper stating this fact, written by this historian in Third Grade, received) they did introduce it to the Europeans.
History of Maize: Charles C. Mann, "What Ancient Maize Can Tell Us About Thousands of Years of Civilization in America," The Smithsonian. November 2018, Retrieved from https://www.smithsonianmag.com/smithsonian-institution/ancient-maize-thousands-years-civilization-america-180970543/
Popcorn specifically: Dale Carson, "Poppin’ Corn for Thousands of Years," Indian Country Today, 8 August 2014, Retrieved from https://indiancountrytoday.com/archive/poppin-corn-for-thousands-of-years-GRqr9n_Rs0Ovrcclvm5q4Q
Stephanie Butler, "A History of Popcorn," History, 22 August 2018 (Update), Retrieved from https://www.history.com/news/a-history-of-popcorn