Is it offensive, or is it just a statement of scientific fact?
Intersex people aren't a third sex category; they're either biologically male (XY chromosomes) or biologically female (XX chromosomes) and will have a sex-specific condition that causes them to be intersex. Intersex isn't a condition itself, it's a general descriptor applied to many different conditions. Some of these conditions may manifest themselves as chromosomal diffrences (XXY males being one of the most common) but are still categorised as affecting either biological males, or biological females.
Caster Semenya, as a person with XY chromosomes, is biologically male. This is fact. Her intersex condition, as the more noticeable ones tend to be, was likely one that caused an abnormality of the genitals and thus she was assigned female at birth.
I don't even know what your stance is on this now. You said earlier that Caster Semenya is a biological female, which isn't true. Then you said it was tautological to say that she is a biological male born with an intersex condition, which, frankly, made no sense. Now you're saying it's offensive to say she's biologically male?