It's not unreasonable that there should be similar stories, given the ubiquity of hunting culture and the brilliant night skies. But consider the number of visible stars and the possible patterns they might be grouped into, and the number of possible interpretations of those patterns. It seems highly unlikely that both the Greeks and the Iroquois would independently group the stars we call Ursa Major into a single constellation associated with a bear. To the modern eye, it looks nothing like a bear, and the stars comprising it might be split into any number of combinations to make other constellations. It seems much more likely that either there was some kind of communication between the two cultures, or that they shared a common mythological origin that preceded both: the article's 'proto-myths', accompanied by proto-astronomy.
Ursa Major is a very common constellation. It's identified in many way by many cultures: it's also common it identify it as a plow, cart, or wagon. To me it's just the Big Dipper.
This is sort of like the birthday problem in statistics: It's overwhelmingly unlikely that two specific cultures would at random choose precisely the same identification. But it's extremely likely that of all cultures, there are two would choose the same identification.
Real evidence of cultural contact between Ancient Greece and the Ojibwe would be a major breakthrough. But this is just random similarities.
