In fact, all price forecasts are guesses, all based on probability, the price band is not artificial, and has a lot to do with the market reaction and heat.
That's true, but it might be that if many forum members keep predicting the same thing, rich newbies start believing in that and buy some bitcoins, thus making the predictions close to reality. I do agree though that there's too much data to analyze and, even though a lot was included in the research, we can't be sure it didn't omit other opinions on the matter. the research does look solid anyway and it is good that people try to conduct them.
It is not purely obvious what the 80% accuracy means. Is it that some kind of an average price prediction is 80% accurate, or is it that almost 80% of predictions are very close to reality?