I think you are right in some respects here. After all, I've always noted that Potential as a function of Age, Level and Performance is very useful. 22 is not old for AA, and Hernandez has played quite well. Now compared to his A-stats, this is a tremendous jump. Now, what the principle of regression to the mean says is that the guy he showed earlier (the guy with a below .700 OPS) is the real him, and that he will turn into that pumpkin eventually.
However (to answer your question - and I am only repeating what the Law or Baseball America sorts say, I have no special talent here), what scouts and FOs want to see is did Hernandez do something (or did he physically grow) where this uptick in performance is bankable and real. If he has had a hot 300 PAs, but is still the same guy ... then that is one thing. If he has done something with his body or swing which has come out in the results? That is a different matter, and one which you start taking very seriously.
Minor league stats are always constrained in their usefulness, just because the games don't count and you don't know what notes the farm director has passed on about stuff the kid should be working on. I have not seen excitement for Hernandez match his performance, but that doesn't mean you are wrong in appreciating the performance.