Were Pygmies discriminated against?

The Mbuti people of Western Africa are the shortest pygmies in the rainforest. Did they become short because of the rainforest environment they lived in? Or did they move to the rainforest because the open plains did not suit people of a diminitive statue? The open plains were more suitable for taller people such as the Masai who could run all day. Maybe short people were discriminated against of moved into the rainforest together thus starting a race of short people.