Why do you think that the President of Iran agreed to being interviewed by Carlson?
I'll offer you a thought: lots of other news organs, and/or interviewers, wanted to get an interview but that's the one he agreed to. Why? Likely to be non-hostile in tone.
But I suggest that you not doubt that President Masoud Pezeshkian was using this (non hostile) interview as an opportunity to get some of his own messaging out. (There's a technique called bridging that sometimes works, and sometimes doesn't).