I always thought a player would have to have some degree of intelligence to be able to improve like this.
In general I think intelligence is used poorly in this game. It doesn't matter in places it should, and matters in places it shouldn't. At least that's the way it seems to me.
Intelligence influences their ability to learn plays as well as make the right decisions during the game. Attribute development improvement like this essentially just means he had more hidden talent than the scouts thought he did.
That was a tough one to pull the trigger on... An amazing 7th round talent, but I have holes to fill with a new plan of attack. Amazingly, he didn't fit into the plan, so...