I think it's a bit of a best case scenario, where they're using a very old game that will run with the lowest allowed 5W TDP with room to spare when locked to 30fps. At that point running the game probably burns so little power you can notice optimizations to stuff like wifi or the controllers. I bet the screen burns more power than the APU in that scenario.

If you're going full blast on a modern game at 30 the power save in percentage is probably trivial, so this seems like a weird combination of factors. But hey, it's a handheld, so every bit helps. Like I said above I just don't know if you'd feel the latency difference in some games where the controller handling is not tied to the display framerate, but I don't know how many PC ports there are where that'd be a thing.