For the next twelve-or-so years, Hyundai technically owned the Kia brand by virtue of being the dominant shareholder. Nowadays, the Hyundai Motor Group only owns about 33% of Kia shares, making Hyundai a minority owner and putting the two automakers on more equal footing.
Of course, the two companies have always operated as though they were independent entities, which may explain the source of your confusion—due to the companies’ partnership, however, their vehicles often share the same platforms and make use of similar technologies.