Good eye, though it's not immediately clear that that's strictly edging in on Carnot efficiencies or if other aspects (two-stroke power cycle, valveless port-based design, eliminating cylinder-head heat loss -- on which, doesn't that eventually reach equilibrium temp
anyway?, etc.) are to credit.
I've seen a few other radical reciprocating energy designs, there are some interesting YouTube vids I should track down. I think "radial engine" might reveal something. New Zealand, possibly Australian engineering firm, IIRC.