I'm going to try to answer this politely, so please take it as genuine response to the idea you've raised. Also note I have no issue with the player or their ability, just the idea you've come up with about PFF numbers.
Scouts look at a wide range of information, but this tends to focus on physical attributes/testing through BLESTO or similar, medical history, their intangibles around leadership attitude etc. through talking to their coaches and others in the programme, but most of all they focus on how they perform on film. How they perform in the good games and the bad games, in adversity as well as in highlight reel mode.
The idea that they rely in any meaningful way on someone else's idea of performance analysis, that's been wrapped up into pretty numbers to sell to a fanbase audience is hard to take seriously.
So no, PFF numbers don't equal draft stock. Which is why his PFF numbers don't equate to his draft stock. Fairly QED.