Here's why:
* Shared Ancestry: Both Manchu and Sibe belong to the Tungistic branch of the Tungus-Manchu language family.
* Mutual Intelligibility: While not fully mutually intelligible, there is a significant degree of shared vocabulary and grammatical features between the two languages.
* Historical Connection: The Sibe people are a group who migrated from the Manchu homeland and have maintained a close cultural and linguistic connection to their ancestors.
While other Tungistic languages like Evenki and Even are also related to Manchu, Sibe stands out as the most closely related language due to its historical and linguistic proximity.