How does Govt. of Bihar defines its people on their website:

"There are tribal as well as non-tribal people in the state. They can
be better classified as non-tribal of north and aborigines of the
south. The latter are tribal in character. The non-tribal group belong
to various castes, prominent among which are : Kayastha, Bhumihars,
Rajputs, and the so-called backward castes. The aborigines belong to
various tribes"

Refer:
http://discoverbihar.bih.nic.in/pages/profile.htm