As neither parent was a diplomat, BoJo was a US citizen by birth. He renounced his US citizenship in 2017.
Technically he could be mislabeled as a U.S. citizen, due to the poorly written & incorrect interpretation of the 14th amendment. The intention of the 14th Amendment was not to make citizens of people who bore children while granted admission into the U.S. on a temporary basis to attend school or hold temporary employment. Nor was the intention for it to make citizens out of people who had entered the country illegally. For a fraudulent act invalidates all.
I contend that the parents of Boris had to officially request that their son Boris be recognized as a citizen of the U.S. to be designated as a citizen. In 1964, the interpretation 14th Amendment was not viewed as it later became to be viewed.