Biology isn't simple. The more biologists study the way the human body works, the clearer this becomes. However, let's not forget that human beings are mammals and it would be extremely odd if we were the only mammal species who couldn't reliably tell on sight, or within a few seconds of watching another human walk, which sex that person is. That's point 1.
Returning to the science, biologists and doctors have stated that disorders of sexual development (DSD) can take many forms but almost all are clearly associated with one sex rather than the other.
So if IK has 5-alpha Reductase Deficiency (not confirmed but would fit the facts in the public domain) that would mean that IK is male and went through male puberty, in spite of having been registered as female at birth. This is extremely rare but not unknown.
If the parents of a newborn can access good paediatric care for a baby born with ambiguous looking genitals, this mistake at registration would not happen (nowadays) because there would be DNA and other tests to find out exactly what was going on, and the baby would be registered with the correct sex. This is the kindest and most sensible thing for the child because at puberty the child's sex becomes unmistakeable.
In cases where the parents are unable to get that level of care, they may be advised or may decide to register the baby as whichever sex seems the likeliest. There is a strong prejudice in some cultures against raising a child as a boy if there isn't a normal looking penis and testicles.
It is a known fact that sports talent spotters look for youngsters with this condition because since the IOC stopped testing for sex, these athletes with F on their passports have often been able to qualify for female teams. The best known example of this is the 800m final at the Rio Olympics where all three of the medallists are now known to have DSDs. https://www.bbc.co.uk/sport/athletics/67367157
It would no longer be possible for athletes with that DSD to compete in women's athletics, and that's right. It's nothing to do with femininity or masculinity. It's to do with having a male body rather than a female body.
As I've already said on this thread, ultimately this is down to the IOC's idiotic decision to stop sex testing. It's no more degrading or humiliating than any of the other tests athletes have to go through. I was taken aback to learn that when they provide a urine sample, to be sure it really is coming straight from their body and not from another (drug-free) person's body, the tester has to observe the athlete urinating. Compared with that, giving a cheek swab is absolutely nothing. It needs to be universal, just as we do criminal records checks on everybody, not just the ones that somebody subjectively thinks look dodgy.