I wonder then what the real percentage of "cash buyers" is.
I'm not sure. Certainly many people refinanced their houses to pull money out over the past few years or got margin loans based on their stocks. Using that money to buy a (different) house still gets counted as a cash buyer.
Cash buyers often finance the property they buy. All a "cash buyer" means is that the deal is not contingent on financing, either contractually or as a practical matter. That is, they can guarantee the sale goes through with cash.