Answer: Confirmation bias
Step-by-step explanation:
The confirmation bias is the ability or tendency of the person to favor, interpret and believe a information based on the previous knowledge and personal believes or based on the assumptions. This is a kind of cognitive bias.
The given situation is an example of confirmation bias this is because of the fact that it is based on presumption rather than understanding based on the facts. Boris being unfamiliar with the concepts of the theory is not able to believe that the theory is true.