Seventy years of brainwashing by the Chinese Nationalist colonization, the regime in exile called Republic of China, has successfully turned the Taiwan residents to believe they are descendant of the Chinese Mainland. DNA scientist Lin Ma-Lin have done stringent scientific studies and found more than 90% of the Taiwan residents actually have Austronesian DNA composition. In the documentary "the Great Human Odyssey," it even points out that 40,000 years ago Taiwan residents start migrating out towards Indonesia, the Philippines, and eastward toward south America.
That is to say, it's very likely southern Chinese people are even Taiwan emigrants.
So how do people falsely think they are Chinese descendants? Because in recorded history, local Taiwanese people turned their family names and ancestry to the ones during Ching empire in order to evade massacre.
Because this administration in Taiwan called Republic of China which no one recognizes worldwide except few poor island countries doesn't want people on Taiwan to know about their bloodline. Besides, people here are too lazy to google. Therefore, this becomes the dumbest nation-scale joke around the world.