[pulkitsh1234]

They claim to detect the neuron action potential (without any physical muscle movements), the relevant section from their demonstration which is pretty cool: https://youtu.be/D8pB8sNBGlE?t=730

So, it's not just the forearm muscles' activity, but the actual neuron impulses.

[frisco]

There is no chance they are detecting extracellular action potentials with their giant skin surface electrodes. This is 100% EMG, which is a potential produced by muscle tissue. They might be able to detect very subtle EMG signals that don't correspond to visual movement, but they for sure aren't detecting APs.