Banyamulenge

Rwandan here: even for me it's confusing because I've heard that there are "rwandaphone" Congolese that are apparently different than banyamulenge even tho they live in the same country.. what's that about , I thought it was just rwanda and Burundi now we got banyamulenge banyarutshuru etc , what's the story behind all that (historical question not political)