Who does Gog & Magog kill "in the sky"?

*We have killed those who are upon the earth. **Let us now kill those who are In the sky** and they would throw their arrows towards the sky and the arrows would return to them besmeared with blood. And in the narration of Ibn Hujr (the words are):" I have sent such persons (Gog and Magog) that none would dare fight against them.* [Sahih Muslim 2937 b] https://sunnah.com/muslim:2937b What does this mean, who is this referring to, who is in the sky? I've searched the internet many times for this but the only results to ever appear are repeats of this hadith.