I don’t think number of registered Dems vs Reps is the point, or even very relevant. The relevant piece is who showed up to vote. In the primary, Dems showed up to the tune of 50% more than Reps.
@MostWanted makes some good points, particularly about the large number of Unafilliated voters, but those are included in the turn out numbers above... heck, I’m one of them.
In the US as a while, the percentage of the population that actually voted has always been rather poor. The numbers have been increasing in the past few elections but were still at a point where simple voter turn out can win elections.