To be honest, I couldn't understand the description of their test (I'm not a statistics major), so I can't comment on their proof.
Just take their word for it, they co-authored the Econometrics bible:
The Econometrics of Financial Markets
Also, from my experience RSI, stochastics, MA-s etc. have no predictive power (tho maybe some traders can generate signals from them using some fundamental info). I even implemented genetic programming that hasn't found anything (basically it evolves logical conditional statements combining various indicators and it is supposed to mimic the way traders think).
However, I found other systems that work and are much more complicated than simple TA. I wouldn't be surprised tho if these will be eliminated or their profitability will be greatly reduced in the next few years.