No, exactly these tribes were invented (as culturally/ racially distinct) by the colonial rulers, first German, then Belgian. Interestingly this is part of the German wikipedia article, but not the English speaking one: https://de.wikipedia.org/wiki/Ruanda#Ethnische_Zusammensetzu...

Edit: It is mentioned a bit in the article about the Hamite theory (a racist theory that formed the academic legitimization for many colonial decisions in Africa): https://en.wikipedia.org/wiki/Hamites