That's a cute idea, but it's extremely unlikely to be true. If nothing else, the human fascination with 7 is a much more likely explanation, especially since 6 is nowhere near as important a number in this way (1,2,3 and 7 are much more common in myths and fairytales).
That's still 90,000 years younger than the supposed story of the 7 Pleiades.
Also consider that no myths survived of much more interesting and recent astronomical phenomena, like the supernova that was visible for a few weeks even in full daylight [https://en.m.wikipedia.org/wiki/SN_1054].
