what is the meaning of the name nyombolo and the ethnic group?

Answer 1

1. It seems to be a surname from South Africa. You can see Nyombolos in these South African websites.
http://www.unisa.ac.za/contents/docs/LostAlumni1_1960.htm
http://www.saimm.co.za/old/pages/papers/papers-v101-n02.htm
2. There's a Nyombolo in this Zambian website too.
http://www.elections.org.zm/new_elections_data/lgcandidates.pdf

I found nothing in the internet about its meaning or tribe, so I think you'd better put your question to South Africans.