Might not be a probe of military capability, but rather a probe of diplomatic stance. US govt is forced to make a statement about the balloon -- which normally they wouldn't care about -- to the public: US govt can choose to either lie and save face for China, saying it was a weather balloon, thus demonstrating earnestness in building relations, or tell the truth and say it was a spy balloon, thus demonstrating unwillingness to paper over such a diplomatic faux pas.