It’s because this article is garbage: of you watch the original German video what he says is
Yuki is ein junger, aufstrebender, vor allem der beste Japaner.
Which translates to
Yuki is a young rising star and the best Japanese driver.
Which reads more like referring to iwasa who is also in the RB juniors program.
I think that interest is added, specifically you pay https://www.irs.gov/payments/quarterly-interest-rates based on the quarters you were missing taxes.
Not sure if the numbers quoted here include that already