We don't know who Obama's father because he has never provided a legitimate birth certificate. His mother was a U.S. citizen.
If you read the article, NEITHER of Vivek Ramaswamy's parents were U.S. citizens at the time of his birth.
Do not waste energy worrying about Ramaswamy’s eligibility. He will be on debate stage and GOP has already accepted his eligibility. Save your energy for more useful tasks such as volunteering to make phone calls for GOP candidates.