MZB based it on MZB's deepest wishes and desires. We really have blessed little to go on in terms of practices, except accounts from the Romans, who make all the Celtic and Germanic deities sound Roman, and from the Greeks, who make them all sound Greek. We have a lot of myths and legends from the Irish and Welsh, but they've been pretty romanticized, and not much is in there about practice anyway.
And of course we have anthropologist's guesses. See deepest wishes and desires, above.
But it's pretty clear that whatever was around Europe in the preChristian era, it wasn't as patriarchal. The accounts of the Celts in particular tend to describe a more equal-opportunity society than the Romans were comfortable with.