You don’t need to be in the stream in person if your Extension doesn’t need it. Many of us just use ffmpeg to broadcast a test pattern while going through the review process.
You’ll need to respond to the email you received. No one here can assist with reviews as the review team don’t communicate regarding reviews outside of those emails.
Explain your situation to them, and that you were live and let them know your channel again just in case they made a mistake and went to the wrong one.