Any encyclopedia will confirm that Kenya was a British colony until December 12, 1963. The Vienna Convention on Diplomatic Relations adopted in April 1961 defines who are diplomats and covered by diplomatic immunity. Nothing in that convention can be construed to cover students. So what you call supposition on my part is actually the result of some research.
Now...do you have anything supporting your supposition that Obama senior was covered by diplomatic immunity?
Actually all it would take to grant him such immunity is someone in the Kenyan colonial government issuing him consular status via his visa, it is not outside of the realm of possibility that he had such.
My supposition negates yours since according to the laws of our country at the time of Obama’s birth citizenship was passed from the father to his children according to the Hague conventions this country had entered into, which by the way also recognized the rights of signatories to disallow dual citizenship as Britain, Kenya, Indonesia and The United States did until fairly recently.
Yet still to this day there are scores of saudi students here on diplomatic passports. They may only have a student visa, but for all that they have diplomatic immunity.