It's strange.
Dele actually broke into the team playing in a 2 with Eric Dier with Dembele in the 10 role. Although not fantastic on the ball, his pressures, box-to-box running and ability to arrive in the box made him one hell of a player.
After scoring a few goals, Poch swapped Dele and Moussa over. But he never became a #10 as such, which always remained Eriksen's role - but more of a dynamic box-to-box player.
I remember when he first arrived there were some stories about how he was the bleep test king in the preseason. When a player has a knack for scoring there's a tendency to just "put them closer to the goal", but It looks like Nuno has gone back and looked at Dele and thought about the kind of player he was when he was successful...he was a runner, and Nuno said as much in his press conference.