IIRC, when you think about words, you also emit weak signals to your face like if you were actually pronouncing those words, but too weak to actually activate your muscles..

This device would pick up those signals.

EDIT: not saying this thing works, but the principle is valid.

From the project's page:

The wearable system captures peripheral neural signals when internal speech articulators are volitionally and neurologically activated, during a user's internal articulation of words.

It doesn't capture the central signal, but peripheral, most likely from the nerves running around your face and your neck used to produce speech.

it's the same bs as facebooks "brain armband" which just picks up signals from muscle activity and not really from the brain. but because the brain is triggering those signals they call it "brain interface". it's just bs.