“Mikan” on its own typically refers to citrus unshiu, but it’s also the name of a larger family of citruses that includes oranges (in fact, oranges are on the chart: of the four surrounding the big one in the middle, it’s the one on the lower left). It’s like how when you say “onion”, you probably mean the bulbous vegetable with the papery skin, but “onions” also includes green onions, welsh onions, leeks etc.