In life, where certainty is much more rare, it is a good rule of thumb to handle doubts this way. By OP's own admission, they can't watch every hour and minute of Charlie Kirk's speeches, interviews, and TV appearances. But he has a clear pattern of making remarks such as this.
Why would you believe that he did not make that statement? Objectivity does not require anyone be neutral for no reason. It is reasonable to assume that the author is correct.