Interstellar Escape

In the fifth year of his career, before Zhan Xin could decipher the repeated signal from the Sirius constellation, his mentor left first. People from the National Security Bureau put him into a black Warrior car and took him to a secret base underground in Lop Nur. There is a perfect titanium-tungsten alloy sphere that cannot be made by humans. Two lines of pinyin are engraved on the sphere with laser: ni hao, li kai. "Hello. Leave." Is it a greeting or a warning? Is it a friendly reminder or a declaration of invasion?