I was wondering the same thing, but based on some clues from a sidebar in the article, it looks like there is real communication:
"The patients were repeatedly asked to imagine playing tennis or walking around their home
"In healthy volunteers each produces a distinct pattern of activity, in the premotor cortex for the first task and the parahippocampal gyrus for the second
"It allowed the researchers to put a series of yes or no questions to severely brain-injured patients. A minority were able to answer by using the power of thought"