I wouldn't underestimate the amount of retail investors that speculated on Bitcoin during that time. It was on major news networks in America, but also on national networks outside the U.S. My uncles and aunts were calling me asking how to buy Bitcoin outside the USA. The FOMO was real back then. Did Tether play a part in the grand pump? I'm sure it did, but I imagine it was more of a catalyst, and not the primary driver as the original study suggested.