Mo Tiange entered the Virtual Sky World when it was time for her to face her core-formation, but she also deliberately placed a stone sculpture puppet outside, disguising it as herself.
Usually, when she cultivated, she could use formations to mislead Lord Daoist Jinghe's divine sense because he wouldn't pay too much attention to her anyway. During her core-formation, however, Lord Daoist Jinghe's divine sense would definitely focus on this place. Considering the secret Virtual Sky World, she better make the illusion a bit more realistic.
Fortunately, she obtained the Xuanji Formation Book, so her formation skills were much better than ordinary people. Her stone sculpture puppet originally had the spiritual aura fluctuations of a late stage Foundation Building cultivator, so it wouldn't be a problem to disguise it as herself with only a few tricks.