The author needs to do more homework...even basic research on the topic would reveal the irrelevance of this question. Nobody denies he had the Kenyan citizenship, which was conferred upon him upon Kenyan independence (based on his father's Kenyan birth.
In fact, the site explains it clearly: “When Barack Obama Jr. was born on Aug. 4,1961, in Honolulu, Kenya was a British colony, still part of the United Kingdom’s dwindling empire. As a Kenyan native, Barack Obama Sr. was a British subject whose citizenship status was governed by The British Nationality Act of 1948. That same act governed the status of Obama Sr.‘s children. "
See Chapter VI, Section 87 (and related) of the Constitution of Kenya.
So you reckon that the reason obama was able to go to pakistan in 1982 is that he went on a kenyan passport?