The Catalauni were a tribe of Belgic Gaul. Etymologically, their name is not connected to the British Catuvellauni so there is no basis to make an equation between the two. Both contain the element catu-, "battle", but apart from that they are only superficially similar: catalauni is composed of catu- + alauno-, "shining in battle", while catuvellauni is composed of catu- + vellauni, "foremost in battle".
References
Catalauni Wikipedia(Text) CC BY-SA