It's common in discussions to use short-hand to identify political beliefs. E.g. a person who is a member of the Republican party would likely call him/herself a Republican. Similarly, Mao or Stalin, who were members of the Communist Party of their respective countries, would call themselves Communists.
Would they follow the "true" political philosophy of Marx? No. Does that mean that they aren't Communists? I don't think so, in the commonly understood meaning of the term (as a way to distinguish membership/belief in a political system).
But arguing semantics like this is pointless. Just as it's pointless to say that, as a hypothetical example, members of the Southern Baptist Convention aren't "true" Baptists because they don't exclusively follow the complete teachings of John the Baptist.
My $0.02.
Cheers,
Scott.