It’s not the potatoes causing the high blood pressure, it’s what we eat the potatoes with. In the case of Finnish Riivinkropsu (shown), it’s eggs, cream, butter, and salt.
I just wrote about a study that linked eating potatoes with having high blood pressure. Even the authors admit it could be what people put on the potatoes, or what they typically eat alongside the potatoes, than any effect of the potato itself.
What do people eat with their potatoes? Salt and fat:
Fanatic Cook 