But would you say that the person who wrote this comes from a Russian speaking area/region in Belarus/Ukraine?
I don't know. On what ground? him/her being able to write Russian? Maybe, but that is not given. Surly you have more info than that.
Belarusians, Ukrainians and Russians are Eastern Slavic.
Never heard about it. The only thing that rings a bell is a eastern Slavic language group that the Rus tribes belonged to about 1000 years ago.