Yes, you missed a potato and it popped leaves this year. Some vars can bloom purplish. They'll keep going for several years if conditions right.

Dan

Seriously, I don't know why potatoes aren't classified as invasive species. This spring we tore out the existing backyard and totally leveled everything with a bobcat. What popped up after the spring rains? Horseradish and potatoes. Everywhere. Even the underdeveloped little pea-sized potatoes will sprout. Perhaps, though, it's because of my mild weather here in California.