They didn't just take a console and slap a solar panel on top and wired that into the battery compartment.
They took a new CPU, buttons, etc. and run an inefficient emulator (goes to show how big the energy budget is) with auto save state before turning off from lack of light/button energy.
Arguably, the former is way more useful in the short run, as you could actually use it for more than ten seconds at a time and retrofit any device easily. But as a research project, the latter is way more useful because it might pave the path to this being viable in the future and having an entirely new class of devices.
it pretty much is, they removed battery and replaced it with direct power supply from solar panels, they mention some additional energy from buttons but I really doubt that would have any meaningful gains, after all how can you generate energy and store it between keypresses unless you will be constantly pressing button in which case you need third hand
