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I suspect that they were once on Smashwords and had been set to "free" when they got removed. I've seen it happen with a couple of other titles which were KDP Selected, where the Smashwords versions were still free for just a few extra days in Sony or one of the other SW-venues right after they'd been removed.
E.g.
Eagle and the Sword (KDP-selected a couple of days ago) and
Dragon and the Unicorn are still showing at $2.99 @ B&N, but not for much longer.