You're right, I must have been confusing Marx with someone else, though now I can't remember who it was that called the Minoans the original communists.
That sounds a like a very strange assertion. It somewhat works with the widespread notion of the Minoans as a peaceful, joyful, somewhat egalitarian and matriarchal society that variously pervaded earlier accounts of Cretan excavations, a view that can be partly blamed on Evans himself, and that is, of course, not likely to be any accurate.
I kind of recall that Christa Wolf (herself a very committed Communist) praised the Minoans to that effect in one of her novel (I think it is Cassandra) but mainly as matriarchal, not as Communist. I suppose she was influenced by Bachofen's ideas about primitive matriarchy (which match somewhhat with Marx-Engelsian ideas about primitive Communism indeed, if one does keeps on the general).
However I am digressing.