The study is saying people couldn’t turn the information into a reliable advantage and your arguing why information leakage might explain why there would be a reliable advantage.
It says that the experienced traders did make money. The OP above is saying that one possible explanation is that the experienced traders simply remembered what happened. As a professional trader myself this seems very reasonable
if you could find an alien civialization with a stock market I'd expect pros to do similiarly well just based on that.
amature traders in the real world tend to be more in tune to rumors and thus more likely to get it right since they had already traded by this sime. (or so I would guess)