I don't think the claim is necessarily that tribal economies are inherently communist, rather that certain groups certainly were. Societies marked by an organizing ethos of "from each according to means, to each according to needs," no class hierarchies, robust social structures and welfare programs, and quite literal communal ownership of means of production -- if we are not going to call that communism, I think we're denuding the term of all meaningful content. I also think we should seriously scrutinize our reasoning for saying, "this was communism over here, but this small tribe or social state can't reallllly be communist." Not impugning your motives in any way, as I wholly agree with your critique as it was stated. I just think we should be careful here.

Personally, I think the most pragmatic thing to do is go case-by-case and distinguish between communism that proceeded capitalism (whatever you'd like to call it) vs Marxist communism, characterized by a transition away from a capitalist state, which is obviously an inherently modern phenomenon.