Mistake?

May be mistake. Normally, after your passport is stamped and local office get your signature and fingerprinting (different from 485 fingerpring), then the card will be mailed to you. Local officer asked you to show theevidence of emergence, suggesting your 485 might not be approved. Every one (not link to GC application) can travel back to China after stamped at local office if emergency occure and need to come back.