Hotcake and pancake mean the same thing today, but historically a pancake was just any kind of batter fried on a pan. The majority of those batters were gritty, hard, and mostly bland. When the modern fluffy pancake batter (which is also waffle batter) started being marketed in English speaking countries, it was called hotcake. It immediately became popular because, well, compared to previous pancakes it was definitely a major improvement. That's why even in the US the phrase "selling like hotcakes" exists. In the US people just stopped using the original name hotcake to refer to fluffy pancake, largely because today almost every other type of pancake has been substituted by the hotcake. In Japan they still use hotcake to refer to it, but most Japanese also understand the term pancake. Souffle pancake/hotcake is a special variant way of cooking that fluffs up the batter into basically a tubular balloon. It's really popular in Japan. It was also trending in the rest of Asia around the 2010s, but never quite caught on.