Ah you're right, they measure the closed eye alpha signal. I'm just skimming with ctl+f and didn't see it, did they mention specifically what electrodes they used for their measurements?
Idk, but the signal doesn't look like an alpha wave you'd get from a good EEG. The video on their repository doesn't seem to be using the normal electrode set, nor use the common procedure of applying the electrodes.
This device can be easily used for machine learning enthusiasts to create projects for controlling robots and mechanical limbs using the power of thought