Not true. She triggered a false positive for T by having more testosterone than the level set out by anti-doping regulations. They wanted her to have less T than the anti-doping limit and so said she has to take drugs to level her hormonal balance to a point set out by WADA. Nothing to do with gender testing. All about drugs.
It has since been raised that there is NO evidence that shows that NATURALLY produced testosterone in women in Caster's condition leads to performance enhancing effects. The effects of synthetic testosterone being injected into normal females is well documented (and hence banned). But this matter is not strictly relevant, for medical reasons.