http://en.wikipedia.org/wiki/File:Uttarpradesh-languages.GIF

http://en.wikipedia.org/wiki/File:Languages_of_Bihar.gif

Now, from the two maps provided, it is clear that Bhojpuri peoples belong to or are a part of Bihari people and peoples of Uttar Pradesh.

http://en.wikipedia.org/wiki/Indo-Aryan_peoples
(see list of indo-aryan peoples)
Peoples of Bihar- magadhas, videhas, angas, mauryas, nanda, pala, gupta, licchavis,
Peoples of uttar pradesh- from Kashi (varanasi), kurus, kolis