This kind of decay requires an overall neutral current that changes the strange quark to a down quark. No such current exists at tree level in the Standard Mod

This kind of decay requires an overall neutral current that changes the strange quark to a down quark. No such current exists at tree level in the Standard Model---instead, strange has to turn into an up-type quark and from there into a down. So, anything from the SM that contributes to this process necessarily involves loops and has no large SM backgrounds. That makes it a very sensitive probe for searching for new physics. Everything seems consistent with the SM but that need not have been---certain kinds of new physics would have stood out in this decay channel. So, while it's not a discovery of a new particle, for example, it is a result that can tightly constrain conjectures.