That's because De Jong is that rare breed of player, who'll just pass you the ball in the exact way you'd want it as a forward. Everybody will combine well with him.
Everyone will combine well with him - until he gets to know the dull Barca style better.
His pass to Dembele following the goal is mere instinct to QUICKLY give a long ball to a fast attacker. He does and did that because he is coming from a different league.
When EV will teach him to prefer possession before anything else, he will stop, wait for the slow guys to come forward, and passes like this will rarely happen.
The same stood for Coutinho last season when playing centrally, partially for Arthur too.
It's a pain to see how many times Dembele - the only one with speed there - tries to make a run but the "possession guys" rather make a safe back-pass...