You know, I would have assumed that they would have done experiments that would reveal the direction of correlation (in the obvious way, i.e., divide the subjects into groups and give each group feedback with varying amounts of positiveness then measure their performance).

But on actually checking that doesn't seem to have been the case at all. Their claims are primarily based on "a mathematical model of consciousness rooted in Boolean algebra", which instantly triggers the "you're doing it wrong" light in my head. (Read the paper yourself before judging, though.)

The linked paper also discusses several experiments, all of which took the form of checking for correlation between positivity and performance during and after the fact, rather than controlling one of those variables.

So you do appear to be correct in your criticism. I'm slightly scared for the state of psychology.