The Federal Supreme Court of Switzerland is an appellate court for the decision from the Court of Arbitration for Sport, so that is why they can "overrule" if they want.
For now, it just means they are suspending the "requirement" on Caster to lower testosterone levels until the appeal is heard (after which they will make a ruling).
The IAAF will get a chance to make their arguments to the Federal Supreme Court of Switzerland as part of the appeal process.